# Trend: lower bottom brackets, pedal strikes and stars



## Charlie Don't Surf (Mar 31, 2017)

This morning for the third time this year, I've went down hard on my favorite local trail. All three were related to hard pedal strikes, today was in a very fast section, and I was getting a run on a few upcomimg obstacles when I got tossed about 25' from a small root that caught me at just the wrong time. This time I JUST missed a large tree with my shoulder, and was seeing stars from the impact with the ground. Anyone else noticing this with the lower bottom bracket trends?


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## Oh My Sack! (Aug 21, 2006)

No doubt, it's a factor with lots of modern geo bikes. My most body damaging get-off that I have had was a pedal-strike induced OTB. Admittedly, I was intentionally weighting a low outside pedal going into a 3mph off camber switchback when I struck the tip of the iceberg, a very well anchored rock tip protruding from the bench cut of the trail. It was insane how powerful the impact was and how quickly I was on the ground and the bike was witnessed doing TWO complete end-over-end rotations before pogo-ing on it's rear wheel and resting nicely against a barb wire fence!

I recently replaced a shock link with one specifically designed to raise the BB on my frame. Seems to be working well.


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## Smithhammer (Jul 18, 2015)

Shorter cranks help. I don't know why so many bikes still come with 175s.


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## stripes (Sep 6, 2016)

Smithhammer said:


> Shorter cranks help. I don't know why so many bikes still come with 175s.


So much this. I run 165s on all my bikes. I'd even consider running 160s, especially on my DH bike.


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## Haymarket (Jan 20, 2008)

It is definitely an issue, something you need to adjust to. I think it is worth it because with the lower BB, bikes handle much better, but riding has to change. I am thinking of going to 165mm cranks to cut down on issues a little bit.


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## Curveball (Aug 10, 2015)

Don't the shorter cranks have less leverage for climbing?


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## stripes (Sep 6, 2016)

Curveball said:


> Don't the shorter cranks have less leverage for climbing?


Not for me. The biggest holdup is my fitness, not my crank length. I run 165mm with a 29.5 inch inseam. About what I should be running.

I rode in Moab last weekend. Only one pedal strike because I misjudged a line. Also I know how to ratchet, which helps. And my bike doesn't have a high bb at all.


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## Oh My Sack! (Aug 21, 2006)

Curveball said:


> Don't the shorter cranks have less leverage for climbing?


They absolutely do. Shortly after my experience I posted above, I bought a Race Face Turbine crankset in 170mm, down from the 175 Sram carbon I had. It worked famously at virtually eliminating pedal strikes on my toothy trail. I was SOLD! About a month into this experiment, I had a revelation and that was that I thought I was losing fitness for some reason. I couldn't figure it out, I was riding all the time but realized I had been struggling on getting up all the chunky tech climbs that I rode multiple times per week. I figured I was just going through some old guy phase so I didn't dwell on it. I was just about to hand over my Sram carbon crankset to a friend that wanted to buy it when I had the bright idea to throw it back on the bike just to see what it felt like in comparison to the 170's I had been riding for more than a month. NIGHT & DAY difference! That 5mm of leverage was amazing! I was back to my old self on the tech climbs. I'm so glad I tried the old cranks. They stayed on the bike and I sold the near new Turbines on pb.


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## Charlie Don't Surf (Mar 31, 2017)

I have to second this ^^^ 
Although, I did like 170mm cranks when spinning SS. Mechanical advantage of a 10mm increase in rotation diameter is what it is, unless you don't fit 175mm cranks to begin with! Today for me was a few things, 1) I was trying to break my PR at the trail since it was 55f, 2) rain yesterday littered the trail with fresh leaves 3) went from Chronicle 3.0's to Nobby Nic 2.8's because of the seasonal trail changes, losing about 1/2" or 12mm of BB height


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## Smithhammer (Jul 18, 2015)

I can still climb anything I climbed with 175s just as easily - short punchy climbs, long consistent slogs, whatever. I know that there is, in theory, a slight leverage loss, but in reality I don't notice any difference at all. The only thing I've noticed that's different is that I'm pedal striking less. Adjust your gearing a bit, if necessary.


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## Lenny7 (Sep 1, 2008)

stripes said:


> Not for me.


Basic physics don't apply to stripes.


Smithhammer said:


> I know that there is, in theory, a slight leverage loss,


 It's actually not a theory at all. It's more of a scientific fact.


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## J.B. Weld (Aug 13, 2012)

Lenny7 said:


> It's actually not a theory at all. It's more of a scientific fact.


Crank length isn't the only component that determines leverage.


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## Smithhammer (Jul 18, 2015)

Lenny7 said:


> Basic physics don't apply to stripes.
> It's actually not a theory at all. It's more of a scientific fact.


Thanks. I science now and then. My point is that in the real world, it doesn't add up to anything the slightest bit noticeable. For me.


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## Lenny7 (Sep 1, 2008)

I agree with you, 175 to 170 probably not. With the same thought 5mm of clearance isn't helping much either. Also, the people talking about 160's, that you would/should notice.
The thing that is interesting to me is how modern geo is geared toward downhill. I would venture to guess the majority of riders don't need slammed BB, a crazy slack HT that look like a "chopper" from the 70's, and enough travel to drop out of an airplane.


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## Sidewalk (May 18, 2015)

Remember, a theory has a ton of science behind it to support it. A hypothesis does not.


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## J.B. Weld (Aug 13, 2012)

There have been studies that show near identical power output from 140-200mm crankarms.


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## bitflogger (Jan 12, 2004)

I don't care about studies except for the informal ones done by a few of us with modern bikes. The performance and fun are so great that we adjust how we ride for the circumstances. 

The marketplace is so full of great stuff and types of bikes and builders that everyone should be able to find happiness.


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## Charlie Don't Surf (Mar 31, 2017)

I think we're getting hung up on minutia regarding cranks and power.... but here's what I remember. Power is the ability to do work, ie- lifting a ton 12'. Torque is the speed that work is done, ie- 5hp with 2 ft/lb torque will do that work in 5 min, where 5hp/9 ft/lb will do it in 2.5 min. Gor most people I (think) the longer arms relate to torque given thats what the leverage advantage would effect. Now... I didn't refer to Google on any of this..... so I might be wrong to 2


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## WHALENARD (Feb 21, 2010)

I love the smell of rock strikes in the morning!


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## Haymarket (Jan 20, 2008)

Lenny7 said:


> I would venture to guess the majority of riders don't need slammed BB, a crazy slack HT that look like a "chopper" from the 70's, and enough travel to drop out of an airplane.


Well, what anyone "needs" is irrelevant. We don't "need" mountain bikes. People want them, and they want "modern" geo, or the bike manufacturers wouldn't have already gone that way or were forced to chase it and ended up there. The market is demanding that geo whether we think people "need" it or not. People want it.


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## Chad_M (Jul 11, 2013)

If your torque at the wheel seems like its less with a shorter crank, go to the next easier gear. 5mm crank length is a small player for the torque output between wheel and ground (chain rings, cassette cog, and wheel size are all huge factors compared to 5mm).


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## Charlie Don't Surf (Mar 31, 2017)

Visual of my morning....


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## JAGI410 (Apr 19, 2008)

WHALENARD said:


> I love the smell of rock strikes in the morning!


Especially with magnesium pedals that give off a nice spark in dry, grassy areas!


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## Haymarket (Jan 20, 2008)

There was a good article on the use of shorter cranks in the current issue of Mountain Flyer. I can't find it online, maybe they don't publish current articles on the page right away. The bottom line was that there aren't really any downsides to shorter cranks, but good upside with reduced pedal strikes. Walt from @waltworks who posts on here was a part of the article.


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## DethWshBkr (Nov 25, 2010)

A 5mm loss doesn't change the leverage much?

Hu. 

A 5mm change in leverage on a rear sprocket makes a massive change....
(Going from a 24 tooth to a 27 tooth on an upshift or downshift for example).
Sure the actual percentage is a little greater, but no one can argue a larger sprocket in the rear is not easier.


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## Smithhammer (Jul 18, 2015)

DethWshBkr said:


> ....but no one can argue a larger sprocket in the rear is not easier.


No one isn't not arguing that.

Numbers are important. Experience is importanter.


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## radair (Dec 19, 2002)

Charlie Don't Surf said:


> I think we're getting hung up on minutia regarding cranks and power.... but here's what I remember. Power is the ability to do work, ie- lifting a ton 12'. Torque is the speed that work is done, ie- 5hp with 2 ft/lb torque will do that work in 5 min, where 5hp/9 ft/lb will do it in 2.5 min. Gor most people I (think) the longer arms relate to torque given thats what the leverage advantage would effect. Now... I didn't refer to Google on any of this..... so I might be wrong to 2


 Torque has nothing to do with speed, it is simply force times distance.


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## justwan naride (Oct 13, 2008)

Both my ht's have low bb's, 305mm on the old one and 300 on the newer one. I also ride both clips and flats and while modern slim platforms give you more clearance, the low overall surface of spd's mean rock strikes are very rare. I've never had one that led to a wipeout using spd's, while with platforms I've had a few scary events. 

Ratcheting is the way to go on tech climbs.

Overall on the hardtails it's not a problem for me, but I guess that on suspension bikes where the bb height is never constant it's more of an issue (it also moves on hardtails due to the fork compressing, but not as much).


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## nhodge (Jul 6, 2004)

Smithhammer said:


> No one isn't not arguing that.
> 
> Numbers are important. Experience is importanter.


Well said.


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## LyNx (Oct 26, 2004)

See my reply below, ignore the vertically challenged, yes, the longer the lever arm (i.e. pedal crank), the more leverage you have, no amount of wishful thinking can change that scientific fact.


Curveball said:


> Don't the shorter cranks have less leverage for climbing?


Yeah, you're also all of what 5'2" ut:  Not everyone tried out for the role of a Hobbit, some of us ate good and as we got older, we grew  Best solution is to look for a bike that doesn't have that low a BB, for me, for an short travel FS, that's no less than 13.25", preferably over 13.5". Also a bike that has a suspension design that sits up in it's travel will help a lot.



stripes said:


> So much this. I run 165s on all my bikes. I'd even consider running 160s, especially on my DH bike.


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## jim c (Dec 5, 2014)

Lenny7 said:


> Basic physics don't apply to stripes.
> It's actually not a theory at all. It's more of a scientific fact.


This guy seems to believe he could move the earth with a lever long enough. I don't, not after seeing how fast I can spin the earth under my low BB bike with short 170mm cranks. I bring the next corner to me so quick it's bigly fast.


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## David R (Dec 21, 2007)

IIRC when I looked into it before making the switch from 175mm to 170mm cranks the figure I found was about a 3% drop in leverage. In other words f--k all especially for someone who is more of a 'sit and spin' sorta guy.

It's pretty obvious that with a lower bb you've got a higher chance of hitting the pedals, but like anything the more you work at focusing on timing your pedaling efforts the better you get at avoiding it.


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## stripes (Sep 6, 2016)

Lenny7 said:


> Basic physics don't apply to stripes.
> It's actually not a theory at all. It's more of a scientific fact.


Yes it does but having hip pain from using too long of cranks for my legs. And I'm a fan of not having pedal strikes.


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## Smithhammer (Jul 18, 2015)

No one is debating physics here. We all are well aware of how levers work and the difference in length between 170mm and 175mm. 

What is being said by almost everyone who has chimed in _and who actually has experience with shorter cranks_ as opposed to just quoting from a high school physics class, is that the difference is barely, if at all, noticeable in the real world. Personally, I noticed no difference at all going from 175 > 170.

This, combined with better pedal clearance is generally worth it, can can help on bikes with lower BBs. 5mm of increased pedal clearance is arguably more noticeable than any leverage loss, perceived or otherwise.


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## stripes (Sep 6, 2016)

LyNx said:


> See my reply below, ignore the vertically challenged, yes, the longer the lever arm (i.e. pedal crank), the more leverage you have, no amount of wishful thinking can change that scientific fact.
> 
> Yeah, you're also all of what 5'2" ut:  Not everyone tried out for the role of a Hobbit, some of us ate good and as we got older, we grew  Best solution is to look for a bike that doesn't have that low a BB, for me, for an short travel FS, that's no less than 13.25", preferably over 13.5". Also a bike that has a suspension design that sits up in it's travel will help a lot.


5'4". Average size for a female.  Riding a small or XS frame with 175mm cranks is awkward. 170mm cranks is wonderful for leverage (I can run a 30t chainring using them), but it's too long of a reach for my legs without creating pain.


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## mikesee (Aug 25, 2003)

Charlie Don't Surf said:


> Anyone else noticing this with the lower bottom bracket trends?


Yep. Seeing more bloody knees, wrists, and elbows on the trails. Hearing about more cracked helmets, wracked nuts, and bruised/broken toes. Talking to more perplexed riders whom don't understand what just happened. Whom thought they knew how to ride, then bought a new bike.

Low BB's make sense for some riders in some places. As with wheel size or tire size or tire pressure, one size does not fit all. I wouldn't take a low BB bike for free, and I define "low" as anything under ~13.5".


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## Lenny7 (Sep 1, 2008)

This^


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## shekky (Oct 21, 2011)

root strikes can be as much of a pain in the ass as rock strikes no matter how low your BB is or what length your crank arms are.

my .02


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## socal_jack (Dec 30, 2008)

Charlie Don't Surf said:


> Visual of my morning....
> View attachment 1162824


Nice sudden stop impulse!


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## lidarman (Jan 12, 2004)

Will we soon look like street monkeys with our 10 tooth chainrings and 60 mm cranks. Gonna be scary when you land a drop and crunch your large cassette cog rather than your rear rim.


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## mountainbiker24 (Feb 5, 2007)

Lenny7 said:


> Basic physics don't apply to stripes.
> It's actually not a theory at all. It's more of a scientific fact.


There may be more leverage from a straighter angle in knee bend from a shorter crank than more knee bend with a longer crank. Yes, a longer crank has more leverage, but overall, the jury is still out.

Like most scientists, you are limiting yourself to a very basic scope of understanding.


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## Charlie Don't Surf (Mar 31, 2017)

mikesee said:


> Yep. Seeing more bloody knees, wrists, and elbows on the trails. Hearing about more cracked helmets, wracked nuts, and bruised/broken toes. Talking to more perplexed riders whom don't understand what just happened. Whom thought they knew how to ride, then bought a new bike.
> 
> Low BB's make sense for some riders in some places. As with wheel size or tire size or tire pressure, one size does not fit all. I wouldn't take a low BB bike for free, and I define "low" as anything under ~13.5".


 I'm wayyy under that!


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## Sideknob (Jul 14, 2005)

I've smashed two pedals to death in recent times. Bloody silly low BB's...high gearing and low BB's = sucky.


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## Chad_M (Jul 11, 2013)

People worried about 5mm of crank length better move their cleats in their shoes to get extra leverage too


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## Charlie Don't Surf (Mar 31, 2017)

socal_jack said:


> Nice sudden stop impulse!


Didn't feel so nice! Lol. So what I've decided to try is a 140 air spring, giving me more up-travel and a bit more BB clearance, and 35mm wide rims on the Nobby Nic 2.8 vs the 45mm they are on, should also cheat some height...


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## Lopaka (Sep 7, 2006)

I upgraded to a new bike with a lower bottom bracket a few years ago. On my first ride over a very familiar trail I had about a dozen pedal strikes. The next day I rode again and had fewer strikes. The next day I had just a few strikes. Within a few weeks, I had no more strikes than I would before I changed bikes

Our brains have a remarkable ability to compensate without conscious thought to new conditions. I didn't change cranks or anything else. I just rode my bike.

Well.......some of our brains have this ability.


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## twd953 (Aug 21, 2008)

I'm still on the fence about shorter cranks. Having run 175s for the better part of 30 years on every bike I own (road, tandem, CX, mtb) they just feel natural to me.

I've been running 165s on my AM FS bike for the past 4 years, while still running 175s on my hardtail. I also run 155s on my DH bike. 

I get the benefits of lower BB on handling, and running shorter cranks in terms of pedal strikes, but my issue is that any time I ride more 2,000 ft of climbing (which is every nearly ride guaranteed where I live) I end up with sore achy knees.

I can do much longer rides with far more climbing on my 175s with no knee pain, and I have experienced the knee pain on two different AM bikes, and was able to repeat it by moving my 165s over to my hardtail.

I've got really long legs (36.5" cycling inseam) so maybe that is part of it? 

Here's one other thing to consider, if you shorten your cranks by 10 mm, you end up raising your saddle by the same 10 mm to end up with the same leg extension when your pedal is at bottom center. So, in your seated position, your C.O.G. is 10 mm higher, which negates the benefit (at least in part) of having a lower BB while seated. 

Now, virtually all of my riding consists of extended climbs followed by extended downhills (we don't have flat pedally trails at all), and I pretty much never sit while going downhill on trail, so a raised C.O.G. while seated is of little consequence to me. But for somebody riding flatter trails that require a lot of seated cornering it might.


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## mikesee (Aug 25, 2003)

Lopaka said:


> Well.......some of our brains have this ability.


If only it were that simple.

I demo'ed a Santa Cruz Hightower in Moab last year. BB was so low for the chunky/ledgy trails there that I was making rock/pedal contact on ~30% of my pedal strokes. Some trails were virtually unclimbable because you just kept smacking pedals. If you're powerful enough to ratchet your way uphill, for miles, on steep grades, more power to you. I don't know anyone that's that powerful.

There are some places where low BB's shine, or are at least tolerable. Sounds like you live in/near one. There are many others where you'll end up walking your bike uphill with that same BB height. You do a disservice to this community by failing to acknowledge that distinction.


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## shekky (Oct 21, 2011)

twd953 said:


> I'm still on the fence about shorter cranks. Having run 175s for the better part of 30 years on every bike I own (road, tandem, CX, mtb) they just feel natural to me.
> 
> I've been running 165s on my AM FS bike for the past 4 years, while still running 175s on my hardtail. I also run 155s on my DH bike.
> 
> ...


one might think you live in northern california near the marin headlands...

extended climbs...extended downhills...


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## One Pivot (Nov 20, 2009)

Crank length is all about biomechanics, not physics. Its a different study, but sort of related. Its not "simple physics" though, by any means. If your body cant apply the power, all the leverage in the world is useless. Think how a 300mm crank would feel. Your knees would hit your chest, you cant apply power like that.

Its extremely easy to *lose* leverage going to a longer crank arm. Your leg angle changes with crank angle... think about how a rear shock is leveraged at different rates through its stroke. Your leg is the same. 

I can apply more power for more duration of crank cycle with a shorter crank. So I apply more power with a 170 vs 175... but not by a whole lot. Over a quite some hours I start to notice how im straining with the 175's via knee pain. 165's work even better for me. That all has to do with biomechanics though. 

Ever noticed how sometimes pushing a technically "harder" gear is both faster and feels like you used less energy? Thats sort of the same. 

If you're under 5'10, it might be the most noticeable going shorter.


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## Sideknob (Jul 14, 2005)

5mm shorter crank arms....a whole 5mm extra clearance.


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## LyNx (Oct 26, 2004)

Not saying not, just the blanket statement that shorter cranks work, is very miss leading when not put into context. It also matters if you're the sort of person who likes to just sit and spin in the easiest gear all day or someone who likes to put down some power in a harder gear, I am the later, hate piddling about on climbs.



stripes said:


> 5'4". Average size for a female.  Riding a small or XS frame with 175mm cranks is awkward. 170mm cranks is wonderful for leverage (I can run a 30t chainring using them), but it's too long of a reach for my legs without creating pain.


To Smithhammer, well yeah, I have never tried a shorter crank, of course not because I don't think they work better, right  I tried 170mm cranks once for a different reason and I could feel the difference in how much torque I could easily output, I actually now run 180mm cranks on my main bike and will upgrade the rest as the old ones wear out _(not sure when that will be going by my going on 13 year old XT cranks)_. If I ever decide I like to spin easier gears all the time, I'll maybe consider going back to a 175mm length.


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## RadBartTaylor (Dec 1, 2004)

Charlie Don't Surf said:


> I think we're getting hung up on minutia regarding cranks and power.... but here's what I remember. Power is the ability to do work, ie- lifting a ton 12'. Torque is the speed that work is done, ie- 5hp with 2 ft/lb torque will do that work in 5 min, where 5hp/9 ft/lb will do it in 2.5 min. Gor most people I (think) the longer arms relate to torque given thats what the leverage advantage would effect. Now... I didn't refer to Google on any of this..... so I might be wrong to 2


Horsepower is all that matter since it's the ability to actually do work. Torque x RPM = HP.

Torque alone is worthless.

That's what is commonly mis-understood, 600 hp is 600 hp, weather that is from a diesel semi truck or turbo 4-cylinder engine.

What you are missing is the gearing component of your equation.

N


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## RadBartTaylor (Dec 1, 2004)

The only time I notice it is when I switch from a bike with higher BB to a lower BB. Yeah I strike pedals more often initially but I learn to deal with it pretty quick and instinctively know when I can and can't pedal. I've never been held back by pedal strikes and can't think of a single situation where it's hindered my ability to get through a section.


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## RadBartTaylor (Dec 1, 2004)

I'm in the it doesn't friggin matter camp. If you were a pro at the pointy end of the stick, sure I get it. For most of us, there may be a light re-learning curve, then no difference within normal bounds. I'm sure going to 155's or 200+ there may be a real bio-mechanical difference, but even then, I'm sure you could adjust quite easily. 

165s to 180s, nothing going to hold any of us average Joes back.


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## Charlie Don't Surf (Mar 31, 2017)

I notice increase in strikes as my speed increases, since I'm heads up riding. Climbing etc I have 54t engagement for ratcheting, it's when I'm really moving when it's a problem


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## OwenM (Oct 17, 2012)

Regarding cranks, it's all about where a given length falls within your range of motion(degree of knee flexion). It doesn't matter if a longer crankarm "has more leverage" if you have less leverage *against* that crankarm.
Talking physics but ignoring biomechanics is missing the forest for the trees. This is a matter of fit, and therefore mechanical advantage or disadvantage, not one length being "better" than the other.


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## stripes (Sep 6, 2016)

OwenM said:


> Regarding cranks, it's all about where a given length falls within your range of motion(degree of knee flexion). It doesn't matter if a longer crankarm "has more leverage" if you have less leverage *against* that crankarm.
> Talking physics but ignoring biomechanics is missing the forest for the trees. This is a matter of fit, and therefore mechanical advantage or disadvantage, not one length being "better" than the other.


Exactly. Everyone gives me grief for riding on 165mm and says I'll get more leverage, but my short legs won't let me take advantage of it.


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## WHALENARD (Feb 21, 2010)

OwenM said:


> Regarding cranks, it's all about where a given length falls within your range of motion(degree of knee flexion). It doesn't matter if a longer crankarm "has more leverage" if you have less leverage *against* that crankarm.
> Talking physics but ignoring biomechanics is missing the forest for the trees. This is a matter of fit, and therefore mechanical advantage or disadvantage, not one length being "better" than the other.


It seems people can't rationalize this vs a study, at least on mtbr. At 6'2" with long legs & long tibia I can not get along with shorter cranks, even 170's. I can feel the difference immediately & gave an entire season to try & overcome any conditioning but they simply don't work for me. With all that said I like short BB's. I've stuffed my feet/ pedal hard plenty of times but the fun factor & control from low BB's is worth it to me. It seems most new bikes are settling in around the same sagged bb height anyway.


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## twd953 (Aug 21, 2008)

shekky said:


> one might think you live in northern california near the marin headlands...
> 
> extended climbs...extended downhills...


Nope, 1 state farther north. But, sometimes I think I live in Northern California because of all of the northern Californians that have moved here. A large percentage of my group of riding buddies are either originally from Norcal or their parents were.


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## pdxmark (Aug 7, 2013)

From my own experience, switching to composite flat pedals really reduced the energy transferred through a pedal strike.


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## RadBartTaylor (Dec 1, 2004)

WHALENARD said:


> It seems people can't rationalize this vs a study, at least on mtbr. At 6'2" with long legs & long tibia I can not get along with shorter cranks, even 170's. I can feel the difference immediately & gave an entire season to try & overcome any conditioning but they simply don't work for me. With all that said I like short BB's. I've stuffed my feet/ pedal hard plenty of times but the fun factor & control from low BB's is worth it to me. It seems most new bikes are settling in around the same sagged bb height anyway.


What do you mean by "dont get along"....pain or speed? Have you actually measured your power output with shorter cranks?


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## Entrenador (Oct 8, 2004)

twd953 said:


> But for somebody riding flatter trails that require a lot of seated cornering it might.


Lots of seated cornering? I must be doing this all wrong.


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## garcia (Apr 10, 2008)

I don't have issues with pedal strikes, but I ride like an old man downhill and through fast stuff, so its a non issue for me. I do, however, think that even if it was, I would keep the 175's and learn to ride differently. I cannot stand short cranks, and can personally feel a difference on a road bike when switching from 172.5 to 175. I tried out 175 when I was building a new road bike years ago, and then went back to a bike with 172.5, and HATED it. Went home, and ordered a new crank.

If the shorter cranks work for you, more power to ya, but I do think to some of us, the difference will drastically impact our climbing ability. At least it would for me!


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## jeffw-13 (Apr 30, 2008)

mikesee said:


> If only it were that simple.
> 
> I demo'ed a Santa Cruz Hightower in Moab last year. BB was so low for the chunky/ledgy trails there that I was making rock/pedal contact on ~30% of my pedal strokes. Some trails were virtually unclimbable because you just kept smacking pedals. If you're powerful enough to ratchet your way uphill, for miles, on steep grades, more power to you. I don't know anyone that's that powerful.
> 
> There are some places where low BB's shine, or are at least tolerable. Sounds like you live in/near one. There are many others where you'll end up walking your bike uphill with that same BB height. You do a disservice to this community by failing to acknowledge that distinction.


Low BB works fine for most of what I ride but when I go rock crawling it's a hindrance for sure.


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## J_Westy (Jan 7, 2009)

Charlie Don't Surf said:


> I think we're getting hung up on minutia regarding cranks and power.... but here's what I remember.
> 
> Power is the ability to do work, ie- lifting a ton 12'.
> 
> ...


Yup -- exactly backwards.

Torque is Work. Force x Distance.

Power is proportional to Torque x rpm. In other words, torque per minute

So torque at the crankset is Leg-Force x Crank-length.

Regardless, it's about biomechanics as stated above. Short legs --> Short cranks, Long legs --> Long cranks.


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## big_slacker (Feb 16, 2004)

This crank length thing is a perfect example of internet debating, haha!

On the topic of BB height I definitely pedal strike more now. I also definitely ride faster up and down on a modern bike, and have way more fun going down. Never crashed because of a pedal strike though, pedals are horizontal and weight back through the gnar.


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## OwenM (Oct 17, 2012)

garcia said:


> I cannot stand short cranks, and can personally feel a difference on a road bike when switching from 172.5 to 175. I tried out 175 when I was building a new road bike years ago, and then went back to a bike with 172.5, and HATED it. Went home, and ordered a new crank.


I'm short, so what makes a "short" crank is relative, but I know where you're coming from. 175s are too long for me, and 170s were an instant improvement.
Just started riding a new bike with 165mm cranks. Fine for spinning, but my initial impression is less favorable for standing and mashing. That's a shame, 'cause my SS hardtail has a low BB, and is where I'd really appreciate more clearance. I don't want to make pedaling it uphill any harder, though!

I filled out some kind of crank length calculator thing awhile back, and it said my ideal crank length was 167.5mm. Maybe it was right!


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## J.B. Weld (Aug 13, 2012)

I have long legs and different formulas have suggested anything from 180-200mm crankarms for me. I've tried 180's and didn't like them much at all, I use 175 for mtb but if I jump on a bike with 170's I don't really notice a difference. 

I put flat (thin) pedals on a bike that I usually rode with spd's and got a lot of pedal strikes on the same trail where I usually had none. I think in addition to low bb's the popularity of fs, which is nearly universal now along with more people using wide flat pedals is contributing to more pedal strikes than before.


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## Oh My Sack! (Aug 21, 2006)

Entrenador said:


> Lots of seated cornering? I must be doing this all wrong.


If he's talking about what I think he is, it's actually a great technique. I do it a lot on my toothy, chunky tight technical switchback climbs where being up at the top of the dropper's stroke creates a high CoG making it difficult to negotiate the technical features smoothly without dabbing or stopping. Dump the post for low CoG and pedal into and through the feature and tight turn in control while seated. Just past the apex, pop seat up to full extension and explode out of the feature. Works like a charm.


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## LyNx (Oct 26, 2004)

As has been stated, a lot also has to do with the way and terrain you like to ride - If you like to spin and it's your go to, ride smoother trails, then shorter cranks might work for you, however if you like to push "bigger" gears and or ride really rough, chunky terrain, shorter cranks most likely won't.


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## Sideknob (Jul 14, 2005)

I was spinning through a fairly tame corner yesterday and bottomed out my left pedal. Dafuq?


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## J.B. Weld (Aug 13, 2012)

LyNx said:


> As has been stated, a lot also has to do with the way and terrain you like to ride - If you like to spin and it's your go to, ride smoother trails, then shorter cranks might work for you, however if you like to push "bigger" gears and or ride really rough, chunky terrain, shorter cranks most likely won't.


I see your point but between the most common alternatives (170-175mm) I don't think it's a deal breaker either way. I doubt in a blind test most people would notice much difference, I don't think I would and I like both (bigger gears/chunky terrain and spinny gears/smooth trails). I think it comes down to personal preference and perceived advantages.


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## Sideknob (Jul 14, 2005)

What if you like to spin small gears in chunky terrain, as in actually go UPHILL?


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## Danimal (Nov 18, 2004)

Sideknob said:


> What if you like to spin small gears in chunky terrain, as in actually go UPHILL?


Which describes a lot of the riding I do.

Semi-related; met a guy out on the trails yesterday who was still riding his 1998 Specialized Ground Control FSR. Couldn't believe how high the bottom bracket was on that bike!

Dan


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## LyNx (Oct 26, 2004)

Get a bike with a higher BB  Personally I find spinning really small gears up those sorts of climbs ends up with you either spinning out or getting pedal strikes because you're spinning too fast. FYI, I LOVE to climb, the techier, the better and hence I run my Banshee FS bikes in the high setting for the taller BB or if I want the angles slacker, a taller fork to slack them out and keep the BB tall so I can run my 180mm cranks 



Sideknob said:


> What if you like to spin small gears in chunky terrain, as in actually go UPHILL?


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## Charlie Don't Surf (Mar 31, 2017)

I've found the solution!! 175mm drive side crank arm, 165 non drive side! Averages out to a 170mm, without the strikes


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## big_slacker (Feb 16, 2004)

Sideknob said:


> What if you like to spin small gears in chunky terrain, as in actually go UPHILL?


I ride a 5010 (fairly low BB) with 175's and love to climb, 2500-5000ft in a ride average. In tech spots pedal strikes aren't the problem so much as having to lean way forward to weight the front due to the slacker geo. More than makes up for that small annoyance on the way down.


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## *OneSpeed* (Oct 18, 2013)

After spending all of my time on 175 for everything, I always felt like I wanted longer cranks on a couple bikes. The SS 29er and the Krampus mostly. Always wanted a longer lever. Granted I'm 6'3" with 35" inseam. 

For some reason I never felt like I wanted/needed longer cranks on my geared HT 29er, or my fatbike, or my cross bike. 

Finally, I recently satisfied my curiosity and got some 180mm XT's for my new SS. I absolutely love them. Bought a second set shortly there after. (180 cranks are hard to come by! Try to find a decent DM 180 crank without some proprietary chainring interface. Go ahead, look.(Raceface, are you listening?!?!?))

I may be building up a Kona Honzo ST over the winter (65mm bb drop). I'm already worried about the BB height. My plan is to run big tires with a 2.6 in front, and possibly go with a 130mm fork. That and 175 cranks should be a great combo.


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## evasive (Feb 18, 2005)

I get mikesee's point - I demoed a Burner prototype at Outerbike 5 years ago, and I was putting my toes on the ground just riding around. I've gotten used to lower BBs in the years since, but when I rode my 5.5 in Moab last week, I definitely noticed the lower BB compared to other bikes I've ridden there. Not so much to do with hitting my pedals, but rather hitting the chainring or frame when climbing ledges. The Yeti definitely isn't a rock crawler. I probably had 4 or 5 minor pedal strikes in a week, but they were incidental, pins-across-rock strikes.



big_slacker said:


> This crank length thing is a perfect example of internet debating, haha!
> 
> On the topic of BB height I definitely pedal strike more now. I also definitely ride faster up and down on a modern bike, and have way more fun going down. Never crashed because of a pedal strike though, pedals are horizontal and weight back through the gnar.


It's not the gnar that gets you - everyone is paying attention to their pedals when sailing through a rock garden. It's the random little rock or root that you hit with a pedal or shoe when you're sprinting along a relatively clear stretch of trail. Strikes like that send you down fast and hard. Lower BBs have made those crashes more common, for me and a lot of people I know. 5mm shorter cranks would probably help.



LyNx said:


> As has been stated, a lot also has to do with the way and terrain you like to ride - If you like to spin and it's your go to, ride smoother trails, then shorter cranks might work for you, however if you like to push "bigger" gears and or ride really rough, chunky terrain, shorter cranks most likely won't.


It's not that black and white. I'm a masher, and I love climbing the jeep road on Amasa Back or similar. I've been happy on 170s for over 5 years. Outside of a SS application, I don't see any reason to go longer.


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## Sideknob (Jul 14, 2005)

LyNx said:


> Get a bike with a higher BB  Personally I find spinning really small gears up those sorts of climbs ends up with you either spinning out or getting pedal strikes because you're spinning too fast. FYI, I LOVE to climb, the techier, the better and hence I run my Banshee FS bikes in the high setting for the taller BB or if I want the angles slacker, a taller fork to slack them out and keep the BB tall so I can run my 180mm cranks


Will definitely be something I seek out on my next bike.


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## Cornfield (Apr 15, 2012)

evasive said:


> It's not the gnar that gets you - everyone is paying attention to their pedals when sailing through a rock garden. It's the random little rock or root that you hit with a pedal or shoe when you're sprinting along a relatively clear stretch of trail. Strikes like that send you down fast and hard. Lower BBs have made those crashes more common, for me and a lot of people I know. 5mm shorter cranks would probably help.


Nailed it! It's one thing to snag a pedal when you're somewhat expecting it might happen, another totally different thing when you're not. I went down so fast there wasn't any time to process what was happening. Luckily I just bruised rib from landing with my elbow between me and the ground.

Kinda hard to see the root I hit, and that's why I didn't and hooked it while I was just cruising along. I ended coming to a stop at that small tree about 10' up the trail.


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## Haymarket (Jan 20, 2008)

Cornfield said:


> Nailed it! It's one thing to snag a pedal when you're somewhat expecting it might happen, another totally different thing when you're not. I went down so fast there wasn't any time to process what was happening. Luckily I just bruised rib from landing with my elbow between me and the ground.
> 
> Kinda hard to see the root I hit, and that's why I didn't and hooked it while I was just cruising along. I ended coming to a stop at that small tree about 10' up the trail.
> 
> View attachment 1163636


How'd you hit that little thing hard with a pedal? Flat ground, not on a turn and it looks like it barely sticks up. What kind of bike and how low is the BB?


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## jcd46 (Jul 25, 2012)

^^^ Is the bike ok?


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## Cornfield (Apr 15, 2012)

Haymarket said:


> How'd you hit that little thing hard with a pedal? Flat ground, not on a turn and it looks like it barely sticks up. What kind of bike and how low is the BB?


IIRC, I had the inside pedal down (my bad) and it felt like the root reached up and grabbed the pedal. It was a rigid SS, Redline Monocog 29er, with a 80mm suspension corrected fork I believe.



jcd46 said:


> ^^^ Is the bike ok?


Yup, good enough to sell for what I paid for it; $200. I put that towards an all-mountain hard tail.


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## *OneSpeed* (Oct 18, 2013)

Cornfield said:


> IIRC, I had the inside pedal down (my bad) and it felt like the root reached up and grabbed the pedal. It was a rigid SS, Redline Monocog 29er, with a 80mm suspension corrected fork I believe.


So at this point in the story I'm thinking to myself "Nice, I knew I liked that guy. No doubt he's a gentlemen and a scholar"



> Yup, good enough to sell for what I paid for it; $200. I put that towards an all-mountain hard tail.


Son of a B&^%$!!! :madman:


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## Cornfield (Apr 15, 2012)

lol, I'm actually seeing a B+/29 steel with the option to run gears/SS in my near future, Onespeed. It just needs to have a higher BB with less drop. I'd be open to another rigid fork, but I don't know of any 120-140 suspension corrected ones.


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## *OneSpeed* (Oct 18, 2013)

That's more like it. Don't sweat the fork, you can easily get a custom Ti fork for $800, no problem.


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## Charlie Don't Surf (Mar 31, 2017)

Cornfield said:


> Nailed it! It's one thing to snag a pedal when you're somewhat expecting it might happen, another totally different thing when you're not. I went down so fast there wasn't any time to process what was happening. Luckily I just bruised rib from landing with my elbow between me and the ground.
> 
> Kinda hard to see the root I hit, and that's why I didn't and hooked it while I was just cruising along. I ended coming to a stop at that small tree about 10' up the trail.
> 
> View attachment 1163636


 Looks a lot like my off at 25mph


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## evasive (Feb 18, 2005)

I don't have a photo of the rock that got me (and my buddy), but it's no more than two inches high, on the outside of the exit of a pair of linked turns. I'd never even noticed it before I hit it. But when sprinting out of the corner, it's in the perfect place to catch a shoe when you're leaned forward sprinting and your toes are pointing down more than usual.


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## cookieMonster (Feb 23, 2004)

Watching out for rocks and roots has always been a part of mountain biking. Even in the days of high BBs, I have a few stories to tell. I broke my right big toe one time snagging a root. I still have bone chips floating around in there.

Another time I snagged the same toe on a rock I'd never seen even though I'd ridden the trail over 200 times. Nearly took me off the bike. Five seconds later the pain was so intense I was actually horrified to take off my shoe to inspect the damage. Blood actually soaked through the shoe -- I'll spare you the rest of the details.

These modern bikes, sure; it's easier to snag a pedal or foot -- especially if you use wide platforms like I do. But honestly I don't notice it except for technical climbs, where a strike usually doesn't result in anything hazardous.

Intense pain has helped me sharpen my pedaling-through-gnar skills considerably-- otherwise the cranks are level and I'm cruising; enjoying the rail-ability of my low BB.


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## WHALENARD (Feb 21, 2010)

Charlie Don't Surf said:


> Looks a lot like my off at 25mph
> View attachment 1163658


I'm confused, is that dog poop you're highlighting?
My only other conclusion is your sag is way off or you have some super weird pedaling issues. Is that into a turn & you were weighting/dropped the wrong pedal? Low bb or not, no way you should strike that in a straight away. Maybe the compression in your shock is blown? Dunno


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## RadBartTaylor (Dec 1, 2004)

J_Westy said:


> Yup -- exactly backwards.
> 
> Torque is Work. Force x Distance.
> 
> ...


That is 100% incorrect. Torque is NOT work, HP is work and why it's really the only useful metric for engines.

600 hp in a Corvette = 600 hp 13L cummins diesel engine in a big rig, they will do the same amount of work and could pull the same amount of weight. One has 4x the torque, but when it comes down to it, they will both provide the same amount of 'work'. It's the reason big rig engines (and all industrial engines) focus on rated HP....not torque.


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## OwenM (Oct 17, 2012)

Cornfield said:


> It's one thing to snag a pedal when you're somewhat expecting it might happen, another totally different thing when you're not.


Yep. don't even bother trying to explain that on here with all these jokers who can't conceive of such commonplace things as pedaling through corners, uphill tech or rock gardens, and talk about ratcheting through climbs, as if they can do that for any distance, 'cause that would just be even more mindboggling to them

When you've got a constant and random scattering of rocks and roots sticking up 4-6" out of the ground and 5" of pedal clearance, all kinds of stuff can happen just pedaling along, or leaning the bike over a little. It's not like I'm having constant pedal strikes or anything, but it's not unusual to get a few, and every now and then one'll take the bike out from under me, or stand me up at a dead stop on a technical climb. C'est la vie...

OneSpeed...good luck with the new bike. Yelli Screamy at 58mm BB drop with 170s here. Even with bigger tires and 10-15mm more A2C with a 130mm fork, you're still not going to be higher at the BB(and mine isn't much over 310mm), not to mention having longer cranks. 'Course whether that's a bad thing or not depends on your trails. Regardless, I wouldn't trade it for my old hardtail with higher BB, longer stays and steeper HTA for anything. I'll gladly take a pedal strike here and there for a much better handling bike that's infinitely more fun to ride, and the geo on that Honzo looks fantastic!


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## RAKC Ind (Jan 27, 2017)

ArizRider said:


> That is 100% incorrect. Torque is NOT work, HP is work and why it's really the only useful metric for engines.
> 
> 600 hp in a Corvette = 600 hp 13L cummins diesel engine in a big rig, they will do the same amount of work and could pull the same amount of weight. One has 4x the torque, but when it comes down to it, they will both provide the same amount of 'work'. It's the reason big rig engines (and all industrial engines) focus on rated HP....not torque.


Sorry man, been an engine tech my entire life, standard gas, performance and commercial diesel.

Your actually about 90% incorrect.

The corvette to cummins comparison has been around for ever and is all but totally incorrect.

Only thing your right about it torque is NOT work, torque is force applied for work to happen.

Horsepower doesnt happen without torque. Torque is the amount of force applied to the crank in this case. The torque applied by each combustion stroke to the crankshaft to rotate it.

Work is the distance traveled while force is applied.

Horsepower is nothing more than the answer to an equation which starts with the torque. You realize a Dyno calculates horse power from torque and rpm right??? And one horsepower is 33000 ft-lb of work in one minute.

Now your analogy...

A 600hp vette is twisting 2-2.5x the rpm of the cummins diesel. Thats because the actual amount of force that vette motor generates is more or less crap. So it has to be twisting high rpms to get the HP. Aka the torque number per single piston, single combustion stroke at 1 rpm SUCKS.

A diesel engine has INSANE torque. But it produces it at low rpms and engine cant spin up like a 600hp vette. Now if said diesel engine could spin up to match rpms of the vette, both torques and hp would make that vette look like a lawn mower engine.

Want high top speed: hp matters most
High initial acceleration: torque
Ability to pull/tow: torque

Btw you know and actually understand what a torque wrench is and how it actually works right?

For cycling, torque is force applied to the crank arm to move it, work is how much force it took to complete a revolution of the crank (torque x distance traveled of crank = work done). Horsepower is amount of work done in 1 minute at a set cadence.

But since HP is not a effective or "motivating" for the power output of a human ( 33000ft-lb of work in 60 seconds), the formula equaling watts is used.

Ok now that I had to correct all that:

Had a reminder of low bb yesturday, freaking toe hurts! Lol. Lean forward a little to dig in the power and forgot not to dip my toes fully. Damn root!

Sent from my SM-G950U using Tapatalk


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## R_Pierce (May 31, 2017)

OwenM said:


> Yep. don't even bother trying to explain that on here with all these jokers who can't conceive of such commonplace things as pedaling through corners, uphill tech or rock gardens, and talk about ratcheting through climbs, as if they can do that for any distance, 'cause that would just be even more mindboggling to them
> 
> When you've got a constant and random scattering of rocks and roots sticking up 4-6" out of the ground and 5" of pedal clearance, all kinds of stuff can happen just pedaling along, or leaning the bike over a little. It's not like I'm having constant pedal strikes or anything, but it's not unusual to get a few, and every now and then one'll take the bike out from under me, or stand me up at a dead stop on a technical climb. C'est la vie...
> 
> OneSpeed...good luck with the new bike. Yelli Screamy at 58mm BB drop with 170s here. Even with bigger tires and 10-15mm more A2C with a 130mm fork, you're still not going to be higher at the BB(and mine isn't much over 310mm), not to mention having longer cranks. 'Course whether that's a bad thing or not depends on your trails. Regardless, I wouldn't trade it for my old hardtail with higher BB, longer stays and steeper HTA for anything. I'll gladly take a pedal strike here and there for a much better handling bike that's infinitely more fun to ride, and the geo on that Honzo looks fantastic!


I can agree with this. Having a low BB on my current bike can be a handful! Its a lot more work than it seems to have to think constantly about pedal placement and when to pedal or not pedal. Or smoking a pedal in the turn on a narrow single track. Mine sits right about 320mm static, and 295mm sagged. I even run 165mm crank to try and alleviate it, which helped but it still can be a challenge.

**and yes, low is all relevant to the person riding the bike, I get that**


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## OwenM (Oct 17, 2012)

Dang, that sure sounds low to me!
The local trail I usually ride a couple times per week is a loop that gets ridden in either direction. With all the roots and rocks, there's a lot of places that I can just stand the bike up on a pedal when wanting to take a picture. I wouldn't want it any lower...























Has smooth and flowy stuff, too, though. It's a *really* fun trail


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## RadBartTaylor (Dec 1, 2004)

RAKC Ind said:


> Sorry man, been an engine tech my entire life, standard gas, performance and commercial diesel.
> 
> Your actually about 90% incorrect.
> 
> ...


I'm well aware of what 'torque' is and isn't, including how HP is calculated from it.

What I said is 100% correct. It's the reason big rigs and all machinery are based on HP. Now you'll see what I didn't say was torque doesn't matter. It helps us understand the characteristics of that power. An engine with good low end torque is good for getting things moving without super lower gears. A engine with horsepower at extremely high RPM is better at high speed application for the same reason, you don't need several gears to get there.

With that said, torque can be corrected for....do you know how? Gearing. All we are talking about is gearing at the end of the axle shaft or at the wheel, through a transmission, splitter, transfer case and axles. That corvette motor can be geared down so much lower than the cummins, probably by a factor of 3+.

Pulling is 100% based on engine HP. Now my example is a bit ridiculous, that corvette motor would be spinning at 6,000+ RPM (with proper gearing to keep in there), wouldn't last long and would get 1 mph doing it, but it's an example to prove the point.

I've seen several arguments like this before - there is a component of semantics involved. Torque and HP can't exist without one another.

You would of had a better argument if you would have started calling me out on things like driveline / engine intertia, power usability, rated vs continuous HP but instead brought up a torque wrench?

Do me a favor, since torque is all that matter to you....lets leave HP out of the equation for a moment. Theoretical example, you want an engine to pull big heavy loads down the highway which one would you choose, leaving durability and longevity out of the equation?

Engine #1: 2500 ft/lbs
Engine #2: 1900 ft/lbs

This should be easy, right?


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## Charlie Don't Surf (Mar 31, 2017)

OwenM said:


> Dang, that sure sounds low to me!
> The local trail I usually ride a couple times per week is a loop that gets ridden in either direction. With all the roots and rocks, there's a lot of places that I can just stand the bike up on a pedal when wanting to take a picture. I wouldn't want it any lower...
> View attachment 1163703
> 
> ...


Looks fun!


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## J_Westy (Jan 7, 2009)

J_Westy said:


> Yup -- exactly backwards.
> 
> Torque is Work. Force x Distance.
> 
> ...





ArizRider said:


> That is 100% incorrect. Torque is NOT work, HP is work and why it's really the only useful metric for engines. .





RAKC Ind said:


> Sorry man, been an engine tech my entire life, standard gas, performance and commercial diesel.
> 
> Your actually about 90% incorrect.
> 
> ...


You're right... I messed up the "Work" part in my post above.

Work is proportional to Torque x Revolutions. In other words, You do twice as much work if you apply the same amount of torque for 2 pedals strokes instead of 1... makes sense -- right.

Here are some good equations if you're interested.

https://www.engineeringtoolbox.com/work-torque-d_1377.html


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## LyNx (Oct 26, 2004)

This is my delema right now, looking for a bit longer and slacker replacement for my '08 Monkey as I've been riding it more and more onb more technical and challenging terrain, but anything that's longer and slacker, pretty much also has some stupid BB drop designed around a 130mm+ fork. My solution is the Kona UNIT frameset, designed around an 80mm suspension fork with a 60mm BB drop, I will then run it B+/29+ with a 29x3" upfront which will slacken out the angles AND raise the BB, win/win. If I put a sus fork on it anytime, it will be at least a 100mm, but more likely a 120mm so BB height won't be an issue.



*OneSpeed* said:


> I may be building up a Kona Honzo ST over the winter (65mm bb drop). I'm already worried about the BB height. My plan is to run big tires with a 2.6 in front, and possibly go with a 130mm fork. That and 175 cranks should be a great combo.





Sideknob said:


> Will definitely be something I seek out on my next bike.





Cornfield said:


> lol, I'm actually seeing a B+/29 steel with the option to run gears/SS in my near future, Onespeed. It just needs to have a higher BB with less drop. I'd be open to another rigid fork, but I don't know of any 120-140 suspension corrected ones.


Same as me, but a tad shorter, always wanted to try 180s, but you can never find them on sale, always MSRP and very limited options. When I find some again on sale I may pick up another set for my other main ride, but feel hard to do that when I've still got 12+ year old XTs going strong.



*OneSpeed* said:


> After spending all of my time on 175 for everything, I always felt like I wanted longer cranks on a couple bikes. The SS 29er and the Krampus mostly. Always wanted a longer lever. Granted I'm 6'3" with 35" inseam.
> 
> For some reason I never felt like I wanted/needed longer cranks on my geared HT 29er, or my fatbike, or my cross bike.
> 
> Finally, I recently satisfied my curiosity and got some 180mm XT's for my new SS. I absolutely love them. Bought a second set shortly there after. (180 cranks are hard to come by! Try to find a decent DM 180 crank without some proprietary chainring interface. Go ahead, look.(Raceface, are you listening?!?!?))


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## RAKC Ind (Jan 27, 2017)

ArizRider said:


> I'm well aware of what 'torque' is and isn't, including how HP is calculated from it.
> 
> What I said is 100% correct. It's the reason big rigs and all machinery are based on HP. Now you'll see what I didn't say was torque doesn't matter. It helps us understand the characteristics of that power. An engine with good low end torque is good for getting things moving without super lower gears. A engine with horsepower at extremely high RPM is better at high speed application for the same reason, you don't need several gears to get there.
> 
> ...


Ok not going to screw up this thread any further. But if you want to "debate" this you need to go back to school to fully understand a few things. Mainly, the reason everything you say has become 100% wrong, you say torque doesn't exist without horsepower. Torque has been around since around the time the wheel was invented. Horsepower has only been around a couple hundred years, since machinery was being invented to replace horses to get work done.

Sent from my SM-G950U using Tapatalk


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## RAKC Ind (Jan 27, 2017)

LyNx said:


> This is my delema right now, looking for a bit longer and slacker replacement for my '08 Monkey as I've been riding it more and more onb more technical and challenging terrain, but anything that's longer and slacker, pretty much also has some stupid BB drop designed around a 130mm+ fork. My solution is the Kona UNIT frameset, designed around an 80mm suspension fork with a 60mm BB drop, I will then run it B+/29+ with a 29x3" upfront which will slacken out the angles AND raise the BB, win/win. If I put a sus fork on it anytime, it will be at least a 100mm, but more likely a 120mm so BB height won't be an issue.
> 
> Same as me, but a tad shorter, always wanted to try 180s, but you can never find them on sale, always MSRP and very limited options. When I find some again on sale I may pick up another set for my other main ride, but feel hard to do that when I've still got 12+ year old XTs going strong.


I do get curious why manufacturers continue pushing BBs stupid low when so many complain. There is a limit. And that limit has done been blown past.

Dont get me wrong, low bb on an XC race bike has merit for sure. But when the rest of us have to increase travel, larger diameter tires, short cranks etc to keep our toes from being smashed its annoying. Especially when you combine that with full suspension.

Sent from my SM-G950U using Tapatalk


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## Haymarket (Jan 20, 2008)

RAKC Ind said:


> I do get curious why manufacturers continue pushing BBs stupid low when so many complain.


I would think because the complaints are a tiny fraction of those riding the bikes, and the net effect of a low BB is people screaming about how good those bikes handle, not about pedal strikes. Look at the highest rated and most popular modern trail bikes...like Hightower, Fuel Ex, Following etc...all with tradtionally very low BBs. Lots of threads about those BBs and pedal strikes, but a lot more threads about how great they are, and how well they handle. The low BB plays a huge part in that.


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## ravewoofer (Dec 24, 2008)

Well, I don't get any of this talk about a low bb,especially the crash photos with tiny, tiny roots and rocks. 

All I know is since I went to the Carbon 429 trail from an aluminum one, I am not smashing into New England rocks and roots. 

There is more travel, and for whatever reason the bike seems to ride higher in the travel negating the low bb. 

I rarely hit a rock, and have never been thrown from the Mach 429 trail Carbon. The same cannot be said for the aluminum version. Had a nice AC separation with that one. 

For sure, the 26ers were rock magnets, but not with the new ones. 

It's just not happening with me. 


Sent from my iPhone using Tapatalk


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## Charlie Don't Surf (Mar 31, 2017)

For me it may be a matter of technique, ie- standing and mashing/ pedaling hard in a corner, toes down or whatever...kinda why I started the thread, just something that I have been experiencing this year on one of my bikes l not sure exactly how its become a crank arm length pseudoscientific debate (your momma so fat she rides 150mm cranks to keep from having belly strikes) etc. But it's been interesting at least


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## mikesee (Aug 25, 2003)

cookieMonster said:


> enjoying the rail-ability of my low BB.


I hear this a lot, often from people that are rationalizing their new bike, and only moments after picking themselves off the ground from a pedal strike.

I wonder, honestly: How much more "rail-able" is your bike than another with a ~1" higher bottom bracket, when both have a 5" dropper and the rider can get their CoG that much lower when railing?

My $.02 is that most would be happier with that 1" higher BB, if they had an opportunity to try it. Dropping your body weight 5" lower via a push of your thumb, when it's really needed, makes a lot more meaningful difference.


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## Smithhammer (Jul 18, 2015)

mikesee said:


> My $.02 is that most would be happier with that 1" higher BB, if they had an opportunity to try it. Dropping your body weight 5" lower via a push of your thumb, when it's really needed, makes a lot more meaningful difference.


It's time for more bikes to be designed with a dropper as an assumed part of the equation which, as you point out, definitely changes some things. Slack STAs and low BB's could largely go away, and I wouldn't miss either of them.


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## MSU Alum (Aug 8, 2009)

mikesee said:


> I hear this a lot, often from people that are rationalizing their new bike, and only moments after picking themselves off the ground from a pedal strike.
> 
> I wonder, honestly: How much more "rail-able" is your bike than another with a ~1" higher bottom bracket, when both have a 5" dropper and the rider can get their CoG that much lower when railing?
> 
> My $.02 is that most would be happier with that 1" higher BB, if they had an opportunity to try it. Dropping your body weight 5" lower via a push of your thumb, when it's really needed, makes a lot more meaningful difference.


Yes. And, on the very rare occasion when I use good technique, that makes a huge difference. Sadly, in that respect, the lightbulb is only flickering.


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## RAKC Ind (Jan 27, 2017)

Smithhammer said:


> It's time for more bikes to be designed with a dropper as an assumed part of the equation which, as you point out, definitely changes some things. Slack STAs and low BB's could largely go away, and I wouldn't miss either of them.


Slack head tubes have little to do with low COG. HTA is totally a preference matter but there is a reason for slacker. More stability at speed.

Personally I hate an overly twitchy front end. Low BBs can stop now. Id be happy with another 8-10mm. How well the low bb rails is really fun, but as said, dropper can accomplish same thing.

Sent from my SM-G950U using Tapatalk


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## big_slacker (Feb 16, 2004)

ravewoofer said:


> Well, I don't get any of this talk about a low bb,especially the crash photos with tiny, tiny roots and rocks.


This for me as well. I ride a lot of roots and rocks here in the PacNW and when I bash pedals it's always a tech spot I'm trying to clear, never at mach speed on a flat or DH. I also looked at some of the geo and my old early 2000's intense tracer was only like half an inch higher than my 5010.

Again, I'm not discounting anyone's experience, just stating my own. For reference this is what I ride on. Not my pics, just googling for the trails to try to show a representative view on the roots/rocks:


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## Smithhammer (Jul 18, 2015)

RAKC Ind said:


> Slack head tubes have little to do with low COG. HTA is totally a preference matter but there is a reason for slacker. More stability at speed.
> 
> Personally I hate an overly twitchy front end. Low BBs can stop now. Id be happy with another 8-10mm. How well the low bb rails is really fun, but as said, dropper can accomplish same thing.
> 
> Sent from my SM-G950U using Tapatalk


I'm not talking about head tube angles. Personally, I like a pretty slacked out front end.

I'm talking about seat tube angles (73º or less). I see no reason for them, particularly on a bike with a dropper.


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## R_Pierce (May 31, 2017)

big_slacker said:


> This for me as well. I ride a lot of roots and rocks here in the PacNW and when I bash pedals it's always a tech spot I'm trying to clear, never at mach speed on a flat or DH. I also looked at some of the geo and my old early 2000's intense tracer was only like half an inch higher than my 5010.
> 
> Again, I'm not discounting anyone's experience, just stating my own. For reference this is what I ride on. Not my pics, just googling for the trails to try to show a representative view on the roots/rocks:


The difference in every single one of your pictures is they arent pedaling. Now reverse that last picture and pedal up it. Let me know how it works then. Here in the midwest we dont have a whole lot of downhill chunder like that, but PLENTY of super tight single track that is riddled with roots or that is sunken into the ground with a berm on each side (think 6-8" wide trail with a 6" hill on each side if you will).

That is where its a bit different for me. I can rail downhill sections like those pictured without a single issue or pedal strike just by keeping them level like in the pictures.

Its a matter of location I do have a feeling.


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## Cornfield (Apr 15, 2012)

big_slacker said:


> when I bash pedals it's always a tech spot I'm trying to clear, *never at mach speed on a flat or DH.*


Just wait till it finally happens to you, then you'll know what we're talking about.


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## richwolf (Dec 8, 2004)

I think the trend is towards capturing the baggy wearing, armor wearing, beer swilling, shuttle riding, park riding, short mileage crowd. Nothing wrong with that but as we see all the time people who are of a different mindset are actually given fewer choices.
Here are a few examples:
1. Shorter chainstays: Great, but what if you are a taller guy and your seat is way high and you are so far over the back of the bike that it is a struggle to keep your front wheel down on long steep climbs? What if you gasp might want to put a rack and pannier on it?
2. Super slack headtube angle: Great for downhill but then unless you want to contort yourself all over your bike how about climbing where the front end wants to wander all over?
3. Then the point of this thread lower bottom brackets: I think that a flat pedal is going to give you more pedal strikes than a small egg beater or spd cause there is more surface area hanging out there. And lots of people are going to flats. I hear of my friends getting pedal strikes all the time on their new bikes particularly on those with FS plus bikes that were just modified from their 29er brethren. A full suspension plus bike should be the ultimate techy uphill rig but a low bottom bracket is going to keep it from reallizing it's full potential.

My Trek Stache has a reasonable head angle that works well both climbing and descending. It also has a higher bottom bracket (I think around 13 inches with 3.0 tires on it). Short chainstays for sure but I run them the way they came (all the way back). I even put a longer stem on it to get my position more forward on it.
Then I go back to my Ti 29er hardtail from 2009 and it works great. So to me this "new geometry" thing is a bit of a marketing ploy that doesn't serve all riders and all terrain equally.

Another big gripe of mine is the one by trend. Right now the most range you can get is 500 percent with the eagle drivetrain which is pricey and replacement cassettes are priced pretty high. Then they rely on a clutch to keep the chain on which leads to stiffer shifting. (I almost always disengage my clutch). Meanwhile my double on my 29er is over 700 percent range. Perhaps someday the double or even triple front rings will be the new rage! No doubt the one by has some things going for it but in my situation where we have long ups and long downs and the fact that I do a lot of bikepacking it is a limiting factor, so much so that I have a double on my Stache that I have to shift by hand, and that is with an 11-46 in the back.


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## *OneSpeed* (Oct 18, 2013)

Smithhammer said:


> I'm talking about seat tube angles (73º or less). I see no reason for them, particularly on a bike with a dropper.


Well I have one example, my most recent frame. All of my previous frames were 21" and required an offset seatpost. Even then my saddle was back of center on the rails. When designing my new custom frame, which is bigger, I wanted to design it around a zero offset seatpost with the intention of adding a dropper. As you probably know most droppers are zero offset only. My STA is 71.75 degrees and really could have been a bit slacker as I'm still using a slightly offset seatpost. It should be fine though I hope.

Granted it's primarily designed as a SS where I'll be standing 90% of the time and STA doesn't mean much, but it's secondary setup will be with gears, a suspension fork, and a dropper.

I also neglected to mention earlier that this frame was intended for longer cranks and I designed it with a 55mm BB drop. So far no issues with pedal strikes.


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## Smithhammer (Jul 18, 2015)

richwolf said:


> 2. Super slack headtube angle: Great for downhill but then unless you want to contort yourself all over your bike how about climbing where the front end wants to wander all over?


I think this is a bit if a misconception, and has a lot more to do with STA than HTA, which is the point I was making above. I've ridden bikes with 65º HTAs that climbed just fine - largely because the STA was 74º, putting the rider in a more centered climbing position and not so far back over the rear wheel. But the trend has been to slacken out STAs in accordance with more slacked out HTAs. There is no real reason for this, especially on an "all around" bike. I think that more often than not, when people complain of a "wandering front end" the real culprit is a STA that puts them too far back on the bike, not the actual HTA.



> 3. Then the point of this thread lower bottom brackets: I think that a flat pedal is going to give you more pedal strikes than a small egg beater or spd cause there is more surface area hanging out there. And lots of people are going to flats. I hear of my friends getting pedal strikes all the time on their new bikes particularly on those with FS plus bikes that were just modified from their 29er brethren. A full suspension plus bike should be the ultimate techy uphill rig but a low bottom bracket is going to keep it from reallizing it's full potential.


Agreed.


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## RadBartTaylor (Dec 1, 2004)

RAKC Ind said:


> Ok not going to screw up this thread any further. But if you want to "debate" this you need to go back to school to fully understand a few things. Mainly, the reason everything you say has become 100% wrong, you say torque doesn't exist without horsepower. Torque has been around since around the time the wheel was invented. Horsepower has only been around a couple hundred years, since machinery was being invented to replace horses to get work done.
> 
> Sent from my SM-G950U using Tapatalk


LOL - 100% wrong....So gearing doesn't multiply torque? Is that the part I got wrong  Or just your failure to understand 4th grade math?

Can't exist without one another based on what we are talking about, in a functional engine....aka you can't have just torque (it wouldn't move) or just hp (since it's a torque based value).

Torque existed WAY before the wheel buddy - since the existence of time. I think you meant HP didn't exist (as we know it) before the wheel.

I do agree with you on one thing - not derailing the thread.


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## LyNx (Oct 26, 2004)

I think this is a Prime example of a lower BB and what can happen when pedaling and you don't see a root/rock or stump that wasn't cut low enough  Don't think Richie Rude was too impressed 



Cornfield said:


> Just wait till it finally happens to you, then you'll know what we're talking about.


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## Charlie Don't Surf (Mar 31, 2017)

I know that feeling!


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## WHALENARD (Feb 21, 2010)

We didn't ratchet through tech ledgy climbs when our bb's were at 14.6"? I personally haven't found lower bb's much of an issue here. I think longer front center & longer wb is a bigger factor for getting bikes up & over super ledgy climbs. Putting the power down on straight aways and having something reach up and hammer my pedal...that I get more of with low bb no question. The rail-ability is real for me. Low bb & short chain stay...yes please! I think riding in the 4 corners is a bit different than loamy Cascadia OR. Variety in both bikes and terrain is good.


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## Sideknob (Jul 14, 2005)

richwolf said:


> I think the trend is towards capturing the baggy wearing, armor wearing, beer swilling, shuttle riding, park riding, short mileage crowd. Nothing wrong with that but as we see all the time people who are of a different mindset are actually given fewer choices.
> Here are a few examples:
> 1. Shorter chainstays: Great, but what if you are a taller guy and your seat is way high and you are so far over the back of the bike that it is a struggle to keep your front wheel down on long steep climbs? What if you gasp might want to put a rack and pannier on it?
> 2. Super slack headtube angle: Great for downhill but then unless you want to contort yourself all over your bike how about climbing where the front end wants to wander all over?
> ...


A couple of points, and by way of background I went from riding XC hardtails since the 90's to a 100mm XC dually to currently a 27.5" 150mm Stumpjumper.

1. Doesn't concern me as I'm short (about 5' 7") but I'm heavy at around 220lbs in my gear. (I've lifted weights for many years.)

2. This did concern me as I like to climb, but it hasn't been a problem. I guess I'm appropriately stretched out and my weight is distributed well for the size bike I'm on.

3. I fitted my old Eggbeaters after smashing an SPD style Exustar pedal body on a small quartz "iceberg" that I never even really saw. A tiny thing really and embedded on a brain dead easy section of trail I've ridden many, many times on several different bikes over the years. Not long after, I ripped one of the "arms" off an Eggbeater...again, on a brain dead JRA bit of trail Currently running cheap Shimano SPD's one of which took a hard whack the other day.... I've found two things to limit me and my Stumpy in certain places - one being the low BB and secondly, the stupid 42T low cog. Just not low enough. In some ways it's like some modern 4x4's - all the traction aids in the world but set low to the ground so soccer moms can enjoy good on-road handling...


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## Haymarket (Jan 20, 2008)

richwolf said:


> I think the trend is towards capturing the baggy wearing, armor wearing, beer swilling, shuttle riding, park riding, short mileage crowd. .


I would guess upwards of 95% of people on the trails fall into at least one or more of those categories you hold in such contempt at certain or most times...so, yeah, I would think the companies would cater to "mountain bikers" who buy bikes.


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## richwolf (Dec 8, 2004)

Haymarket said:


> I would guess upwards of 95% of people on the trails fall into at least one or more of those categories you hold in such contempt at certain or most times...so, yeah, I would think the companies would cater to "mountain bikers" who buy bikes.


You actually left out the part where I said nothing was wrong with that. In actuality many of my mountain biking friends fit many of those criteria and they hold me in more contempt than I do them!

Why would the mountain bike companies want to go after a share of just what I was buying?? They have to market to the masses. For example I don't get the whole beer and bike festival thing but most do.

Crank length, Rim widths, tire pressures, tire width arguments are all fine and good but when it comes right down to it the rider and their fitness trump all. (no reference to the donald!)


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## mountainbiker24 (Feb 5, 2007)

It's obvious to me that location and rider preference dictate ideal geometry. I don't really understand why people keep arguing about this type of thing. If you want your bike to rail corners and add stability for a variety of reasons, then you probably prefer a lower bottom bracket. If you pedal through a lot of rocks, roots, and offcamber terrain, you probably would prefer a higher bottom bracket at the expense of a little stability. It's not all that difficult for an experienced rider to compensate either way. 

Personally, I pedal through enough chunk that I prefer a bit higher bottom bracket, and I'll let my bike handling skills compensate for the compromises. I'd rather be a tiny bit slower through the corners and flat out downhills and gain speed through pedally rock gardens and roots while (hopefully) avoiding the random pedal clip. I had a pretty good one a couple years ago. I thought I broke my femur on that one, and I'd rather not do that again.


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## milehi (Nov 2, 1997)

I've never had a problem with low BBs. I've had several custom six inch travel bikes with "current geometry" built since 2006 for Super D and Enduro racing. My current rig's BB is 13.1".


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## R_Pierce (May 31, 2017)

Vader said:


> I've never had a problem with low BBs. I've had several custom six inch travel bikes with "current geometry" built since 2006 for Super D and Enduro racing. My current rig's BB is 13.1".


Static or sagged? What is the BB height while sagged?

Sent from my ONEPLUS A3000 using Tapatalk


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## Charlie Don't Surf (Mar 31, 2017)

sometimes it is just three low BB placement, not technique, outfit style or size of your plums... I'm hauling ass on my 140mm HT on this trail in some pseudo gnar, yet I've still went down due to stray pedal strikes on mellow terrain


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## milehi (Nov 2, 1997)

R_Pierce said:


> Static or sagged? What is the BB height while sagged?
> 
> Sent from my ONEPLUS A3000 using Tapatalk


That measurement is static. I'm not sure what it is sagged. I also have always used a coil shock if that makes a difference. Here's the first bike I had built with current geo in 2006. 24TT, 67HA 73.5 SA and 13.5BB


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## R_Pierce (May 31, 2017)

Vader said:


> That measurement is static. I'm not sure what it is sagged. I also have always used a coil shock if that makes a difference. Here's the first bike I had built with current geo in 2006. 24TT, 67HA 73.5 SA and 13.5BB


What's the rear travel and the shock size?

Sent from my ONEPLUS A3000 using Tapatalk


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## milehi (Nov 2, 1997)

R_Pierce said:


> What's the rear travel and the shock size?
> 
> Sent from my ONEPLUS A3000 using Tapatalk


Six inches of travel using a 7.87X2.25 shock. I had a Custom Romic shock, a DHX with Push's MX tune and a CCDB, all with Ti springs


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## WP Local (Jun 25, 2006)

LyNx said:


> I think this is a Prime example of a lower BB and what can happen when pedaling and you don't see a root/rock or stump that wasn't cut low enough  Don't think Richie Rude was too impressed


tucked and rolled like a pro!


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## big_slacker (Feb 16, 2004)

R_Pierce said:


> The difference in every single one of your pictures is they arent pedaling. Now reverse that last picture and pedal up it. Let me know how it works then. Here in the midwest we dont have a whole lot of downhill chunder like that, but PLENTY of super tight single track that is riddled with roots or that is sunken into the ground with a berm on each side (think 6-8" wide trail with a 6" hill on each side if you will).
> 
> That is where its a bit different for me. I can rail downhill sections like those pictured without a single issue or pedal strike just by keeping them level like in the pictures.
> 
> Its a matter of location I do have a feeling.


Same stuff on the way up BTW. 

I get what you're saying, if you read the post you quoted there you can see me agreeing with you about when I pedal strike. But it just doesn't bother me that much for the few times it happens vs the fun on the way down with a lower, slacker bike. I think you can't have it all, and trail bikes particularly are a compromise. I feel like the current crop do a pretty damn good job and being very capable up AND down. Sep this year I rode a 12 hour epic (there were probably pedal strikes on the uphill tech) and the next weekend I was in the park doing jumps and drops with no configuration change.


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## cookieMonster (Feb 23, 2004)

Well, my bike is five years old, so I'm not really trying to justify the purchase anymore. And I have always dropped my seat for descents even before droppers, so that's not a factor here.

Comparing my current bike to my older long travel bike (both 180mm travel at both ends) and similarly slack head angles, I am way faster at cornering on the new one which has a considerably lower BB height. A big part of my enjoyment of descending comes from how fast I can slam turns. The lower COG of these modern bikes is noticeable and measurable in time saved. I have been riding and racing DH for 20+ years. The difference is real. I'm faster now than I've ever been, and it has nothing to do with suspension performance. I attribute it to geometry being optimized.


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## TiGeo (Jul 31, 2008)

Low/long/slack is what everyone should be riding. Drink the koolaid, it's good for you (sarcasm). Like 29ers, this trend will push the boundaries and then at some point, things will bounce back a little to a more reasonable reality for most folks. Some of the bikes I see folks riding on our local trails are almost funny they are so slacked out..."I can't climb that stuff that well"...well no ****.


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## singletrackmack (Oct 18, 2012)

I don't see any mention of suspension set up (especially sag), although I may have missed it. 

There can be a huge difference in BB height while riding on the same bike depending on sag. A 150mm fs bike will change BB height by over an inch going from 10% to 30% sag. Plus, how the suspension is set up can change how it sits in the travel while pedaling. For example, using the pedal pro on my RP23 and more compression on my fork helps the bike sit higher in its travel while riding which is good for helping to avoid pedal strikes in rough.


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## *OneSpeed* (Oct 18, 2013)

This thread jinxed me, I'm sure of it. There I was, JRA, and WHAM! Next thing I know I'm up over the handlebars, half inverted, and headed at a tree. Bounced off the tree and landed back on the bike, in a pile. Things hurt but I don't think bones are broken. Untangle myself from the bike and get to my feet. Both my lights were knocked from their perch. Picked up one light and checked myself and the bike for major damage, nothing major but I'll be soar for a couple days. 

It wasn't a BB height issue, there's leaves on the ground and I just didn't see a stump that stuck up 4-5". Totally my fault, and I paid for it. I think the bike came out better than I did, and that's the way I prefer it. 

Damn, I hate how quickly and violently a pedal strike can turn a dull moment into a OneSpeed pile of pain and blood, not to mention the damaged ego.


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## elder_mtber (Jan 13, 2004)

Torque is not work. Torque is a (twisting) force. Like you are torquing a head bolt - it might feel like "work" or effort to the human, but is not work in the physics sense. Now, if the torque was lifting a bucket of water, that would be work.


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## tedsti (Oct 22, 2004)

It is interesting that people are trying to solve the low BB "problem" by running shorter cranks. One of the reasons to go to a lower BB is to lower the center of gravity. When you put short cranks on the bike, you will raise your saddle the same amount you shortened your cranks and bring your center of gravity back up. So you now lost the benefit of low center of gravity and you are running shorter cranks which may be a detriment. Shorter cranks are not a fix, they are a band-aid at best that may have adverse side effects.


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## RAKC Ind (Jan 27, 2017)

tedsti said:


> It is interesting that people are trying to solve the low BB "problem" by running shorter cranks. One of the reasons to go to a lower BB is to lower the center of gravity. When you put short cranks on the bike, you will raise your saddle the same amount you shortened your cranks and bring your center of gravity back up. So you now lost the benefit of low center of gravity and you are running shorter cranks which may be a detriment. Shorter cranks are not a fix, they are a band-aid at best that may have adverse side effects.


The people that do this DONT CARE lol. They know what it does, They would rather have the slightly higher COG (easily compensated for especially with a dropper post) to reduce pedal strikes and resulting crashes.

Lower BBs arent for everyone and when its really hard to find a decent new frame with a higher BB, ways to "fix" the problem become priority.

Not everyone rides places where the benefits of a low BB outweigh the drawbacks. And with dropper posts everywhere now, really low BB isnt necessary anymore.

Sent from my SM-G950U using Tapatalk


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## evasive (Feb 18, 2005)

tedsti said:


> It is interesting that people are trying to solve the low BB "problem" by running shorter cranks. One of the reasons to go to a lower BB is to lower the center of gravity. When you put short cranks on the bike, you will raise your saddle the same amount you shortened your cranks and bring your center of gravity back up. So you now lost the benefit of low center of gravity and you are running shorter cranks which may be a detriment. Shorter cranks are not a fix, they are a band-aid at best that may have adverse side effects.


I don't care about my COG when I'm on the saddle.


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## Haymarket (Jan 20, 2008)

tedsti said:


> When you put short cranks on the bike, you will raise your saddle the same amount you shortened your cranks and bring your center of gravity back up.


Seated center of gravity that goes up by raising the saddle is not really the critical thing here....when you're standing on the level cranks, COG is the same as with long or short cranks...if you're sitting, it doesn't really matter. You don't rail turns or fly down sitting....


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## RadBartTaylor (Dec 1, 2004)

I'll preface this by saying I've never ridden in the NE or Midwest, but living in Oregon, I always considered our terrain fairly rooty and rocky, not contiguous on all trails, but fairly consistent at times among many of them.

I've never once had an issues with pedal strikes once I get used to a bike. Rode a HT for years, recently got a FS and did hit my pedals a couple times, but I'm over it. For me it's seems to be a technique thing. Maybe it's because I rode trials for years and ratchet if required, not sure, but I don't actively think about if/when I'm going to hit a pedal.

With that said, I rented a FS bike in Utah several years ago for a weekend, coming off a HT, so was not used to it. Had a brutal rock strike crash. The rest of the weekend had a couple minor ones, but towards the end of riding I was figuring things out and rock strikes all but went away.

I run 180s on a long wheel base bike with a moderate BB drop so have fair reason to hit, a lot.


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## RadBartTaylor (Dec 1, 2004)

RAKC Ind said:


> The people that do this DONT CARE lol. They know what it does, They would rather have the slightly higher COG (easily compensated for especially with a dropper post) to reduce pedal strikes and resulting crashes.
> 
> Lower BBs arent for everyone and when its really hard to find a decent new frame with a higher BB, ways to "fix" the problem become priority.
> 
> ...


That's not correct.

Dropper posts effect COG MASSIVELY, by several inches. BB's vary by what, an inch or so? One is much more impact than the other. Not to mention, droppers get the seat out of your way which aids your ability to move around on the bike. They don't offset one another.

BB drop really effect how a bikes turn and hold lines, which can be (in a lot of cases it is) independent of seat height.

I'm not convinced low BB's are the best. It's still a big argument in the Cyclocross circles, low vs high. In general low BB corners more predictably in the faster sweeping corners, high BB are more maneuverable in tight corners and allow for pedaling earlier through corners. Ain't no dropper posts in cross (yet).


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## evasive (Feb 18, 2005)

ArizRider said:


> Ain't no dropper posts in cross (yet).


I take it you didn't get this email:


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## 127.0.0.1 (Nov 19, 2013)

J.B. Weld said:


> There have been studies that show near identical power output from 140-200mm crankarms.


fine. I would assume so. but now measure torque. longer arms generate more torque for same power.

which is why my SS has 180's on it


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## TiGeo (Jul 31, 2008)

Amanda Panda...RAD!


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## @[email protected] (Aug 25, 2017)

J.B. Weld said:


> There have been studies that show near identical power output from 140-200mm crankarms.


What do they show about torque output though?


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## mikesee (Aug 25, 2003)

@[email protected] said:


> What do they show about torque output though?


Torque output will depend on your gearing.

I think the word you're looking for is leverage. Shorter cranks change the leverage ratio slightly, which you can compensate for by shifting, thereby varying the torque output. It's a moving target. Moving your cleats makes a difference, too.


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## @[email protected] (Aug 25, 2017)

mikesee said:


> Torque output will depend on your gearing.
> 
> I think the word you're looking for is leverage. Shorter cranks change the leverage ratio slightly, which you can compensate for by shifting, thereby varying the torque output. It's a moving target. Moving your cleats makes a difference, too.


No, torque at the crank is what I was referring to.


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## bronxbomber252 (Mar 27, 2017)

Power is the more important number as it reflects the ability to do work (move mass a distance). While torque at the BB will be less with the shorter crank given the same force at the pedal, the force a person can apply to the pedal will vary with crank length and it will be different for each person's proportions. Further if the person can spin the cranks faster with shorter cranks then that can offset the torque reduction because power is a function of torque and RPM.


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## RadBartTaylor (Dec 1, 2004)

bronxbomber252 said:


> Power is the more important number as it reflects the ability to do work (move mass a distance). While torque at the BB will be less with the shorter crank given the same force at the pedal, the force a person can apply to the pedal will vary with crank length and it will be different for each person's proportions. Further if the person can spin the cranks faster with shorter cranks then that can offset the torque reduction because power is a function of torque and RPM.


Exactly and why power (in the context of cycling WATTAGE), just like it is in cars, is the important factor as shifting can vary the torque output at the wheel / axle.


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## Sideknob (Jul 14, 2005)

Seems like manufacturers are embracing the low BB and stupid-high 11-42 1x11 cassettes despite what every off-road vehicle user knows - low gearing and clearance are vital.

I literally can ride my old 100mm forked 3x9 XC hardtail up steeper rocky chutes than I can ride my 150mm AM bike and it all comes down to pedal clearance and gearing.


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## TiGeo (Jul 31, 2008)

^^^I just don't see how a 11-42 cassette paired with a 30t chainring is "stupid high" - that is a low-ass gear. Just went to Eagle and a 32/50 is so low it's almost not useable.


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## Sideknob (Jul 14, 2005)

TiGeo said:


> ^^^I just don't see how a 11-42 cassette paired with a 30t chainring is "stupid high" - that is a low-ass gear. Just went to Eagle and a 32/50 is so low it's almost not useable.


It's stupid high if you're heavy and like to ride steep and at times technical rocky uphills.

Presumably all those folks throwing away 11-42's for aftermarket 46 or lower geared options agree.


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## bronxbomber252 (Mar 27, 2017)

Sideknob said:


> It's stupid high if you're heavy and like to ride steep and at times technical rocky uphills.
> 
> Presumably all those folks throwing away 11-42's for aftermarket 46 or lower geared options agree.


10-42 with a 28T chainring is roughly the same range as 11-46 with a 30T


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## acedeuce802 (Jun 30, 2017)

ArizRider said:


> Exactly and why power (in the context of cycling WATTAGE), just like it is in cars, is the important factor as shifting can vary the torque output at the wheel / axle.


Just seconding that power matters, torque at the crank doesn't. Another way to think about it is that power is the same at the crank and the cassette. Torque gets multiplied or divided by gear ratios. You can do the math to prove that a shorter crank arm will have less torque, but will be spinning faster and have a different gear ratio, that will end up having the same torque at the wheel. But the really easy way to think about it is the equation that relates power and torque, and to think about power at the wheel. HP = TQ X RPM / 5252. If you compare 2 bikes that are going the same speed, then RPM at the wheel is constant, meaning that if HP increases so does torque and vice versa. If the bike with 140mm cranks can output the same power as the bike with 180mm cranks, then the torque at the wheel will be the same. It doesn't matter what's going on at the cranks, power/torque at the wheel is all that matters.


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## RadBartTaylor (Dec 1, 2004)

acedeuce802 said:


> Just seconding that power matters, torque at the crank doesn't. Another way to think about it is that power is the same at the crank and the cassette. Torque gets multiplied or divided by gear ratios. You can do the math to prove that a shorter crank arm will have less torque, but will be spinning faster and have a different gear ratio, that will end up having the same torque at the wheel. But the really easy way to think about it is the equation that relates power and torque, and to think about power at the wheel. HP = TQ X RPM / 5252. If you compare 2 bikes that are going the same speed, then RPM at the wheel is constant, meaning that if HP increases so does torque and vice versa. If the bike with 140mm cranks can output the same power as the bike with 180mm cranks, then the torque at the wheel will be the same. It doesn't matter what's going on at the cranks, power/torque at the wheel is all that matters.


Yes sir.


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## WHALENARD (Feb 21, 2010)

acedeuce802 said:


> Just seconding that power matters, torque at the crank doesn't. Another way to think about it is that power is the same at the crank and the cassette. Torque gets multiplied or divided by gear ratios. You can do the math to prove that a shorter crank arm will have less torque, but will be spinning faster and have a different gear ratio, that will end up having the same torque at the wheel. But the really easy way to think about it is the equation that relates power and torque, and to think about power at the wheel. HP = TQ X RPM / 5252. If you compare 2 bikes that are going the same speed, then RPM at the wheel is constant, meaning that if HP increases so does torque and vice versa. If the bike with 140mm cranks can output the same power as the bike with 180mm cranks, then the torque at the wheel will be the same. It doesn't matter what's going on at the cranks, power/torque at the wheel is all that matters.


It's not all that matters & the automotive analogies do not apply as the engine remains the same. Regarding crank length and leverage "all that matters" is femur & tebia length and the ratio between the two. One size doesn't fit all here.


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## acedeuce802 (Jun 30, 2017)

WHALENARD said:


> It's not all that matters & the automotive analogies do not apply as the engine remains the same. Regarding crank length and leverage "all that matters" is femur & tebia length and the ratio between the two. One size doesn't fit all here.


Sure they apply, power is power, torque is torque. Doesn't matter if it's a crankshaft or a crankset. If the ratio between femur, tebia, and crank arm length are not ideal, then power will be reduced, thus torque at the wheel will be reduced. If it is proven that power remains the same between 140mm and 180mm cranks, then torque at the wheel is the same and acceleration will also be the same.


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## mikesee (Aug 25, 2003)

Charlie Don't Surf said:


> Anyone else noticing this with the lower bottom bracket trends?


This thread and it's many ramifications were on my mind a few nights this week while riding.

One of the other trends I've noticed with low BB's is trail sanitization. Bear with me.

What I've been noticing are lots more chainring and pedal scrapes on embedded rocks that have been a part of the trail tread for decades, but are only now getting scraped or impacted.

Some of this is erosion -- the trail is eroding around the rock, bringing it more 'up' into play. This happens pretty slowly.

And then there's the erosion of BB height by manufacturer mandate. And this has happened so much faster that it's pretty easy to see, feel, even measure the effect.

None of the above is really up for debate -- it's happening, and readily observable.

What I keep noticing though, and that's really jumping out now that I've been able to link cause with effect, is that lots of in-trail rocks are being dug out, little by little, by low-BB riders clipping them repeatedly. Eventually, unless they're bedrock, they come loose, and then someone stops, works on it for a moment or two, and when it comes free they toss it out of the trail. Voila, the trail just got easier.

That's one thing.

The other thing is that embedded boulders or slabs *next to* the trail keep ending up *in* the trail, by the same cause. I came across two of these tonight -- one was a ~12" x ~18" x ~3" thick slab that was dead-center in the trail, and you could clearly see the spot adjacent to the trail where it'd lived for decades or centuries -- until just hours or minutes before. Just past one of them you could see where the rider had fought to keep control, and then the front wheel knifed, and then the inevitable body print and slide, then lots of footprints-going-in-circles as they'd dusted themselves off, checked the bike, and tried to understand what just happened. The second one I couldn't see where/if a crash was caused.

In neither of these instances is anyone setting out to sanitize the trail. But because they keep making contact with the embedded rocks, loosening them, and ultimately getting them removed, the trails are getting easier.

We already have land managers dumbing trails down to suit the least common denominator. And then there's the least common denominator occasionally/often taking it upon themselves to bring the trail down to their level. Now we have manufacturers complicit, admittedly unintentionally, in removing challenge from trails.

Death by a thousand cuts.


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## scrublover (Dec 30, 2003)

(takes his Nomad3 and 5010 27.5 bikes running 26" wheels on rooty rocky slow and fast stuff and slooooooowly backs away from thread...)


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## gooseberry1 (Mar 16, 2016)

I was able to ride a chumba way back and that was my main issue. Ok this was in the 90’s and I did end up in the top of a tree out in corona but it’s still a issue 


Sent from my iPad using Tapatalk


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## Charlie Don't Surf (Mar 31, 2017)

my wife's brand new 2018 Loki 130mm 650b came with 170mm Turbine cranks.



But, they are drilled at 170....arm length is the same as the 175 lol


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## *OneSpeed* (Oct 18, 2013)

Charlie Don't Surf said:


> But, they are drilled at 170....arm length is the same as the 175 lol


Most are. I almost brought this up earlier but didn't want to cause another argument in a strongly opinionated thread.


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## LyNx (Oct 26, 2004)

Why do you fvckers always try to work an argument to suit you instead of just stating obvious basic facts with everyone running the same, which makes everything neutral and then factor in the longer cranks or shorter cranks??

When you are honest and not trying to skew facts, you realise that if person A has 160mm cranks and is turning a 23 inch gear @ 200WATTS and person B is running 180mm cranks and turning the same 23inch gear @ same 200 WATTS, the person with the longer cranks is putting out more torque with less RPMs so the person with the shorter cranks will have them to spin faster, thereby possibly smacking one of those rocks we all encounter, thereby stalling them or making them dab, fairly fvcking simple when you're honest.



acedeuce802 said:


> Sure they apply, power is power, torque is torque. Doesn't matter if it's a crankshaft or a crankset. If the ratio between femur, tebia, and crank arm length are not ideal, then power will be reduced, thus torque at the wheel will be reduced. If it is proven that power remains the same between 140mm and 180mm cranks, then torque at the wheel is the same and acceleration will also be the same.


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## Charlie Don't Surf (Mar 31, 2017)

*OneSpeed* said:


> Most are. I almost brought this up earlier but didn't want to cause another argument in a strongly opinionated thread.


This is the first set I've had of RF cranks, all my Sram sets were, eh, normal? Makes sense cost wise though. Is be double pissed if I bought them because of this thread, and they were still 175 lol


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## *OneSpeed* (Oct 18, 2013)

Charlie Don't Surf said:


> This is the first set I've had of RF cranks, all my Sram sets were, eh, normal? Makes sense cost wise though. Is be double pissed if I bought them because of this thread, and they were still 175 lol


Maybe I shouldn't have said "most", but many shorter cranks are just re-drilled 175's.


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## NorCalTaz (Nov 12, 2013)

I always have run 175mm cranks on my last three bikes which had BB heights of 13" - 13.4" inches, so my frame of reference (pun intended) is limited. I don't have many pedal strikes that are significant, although looking at my XT pedals says different. Thinking technique improvement rather than gear is the answer.


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## RadBartTaylor (Dec 1, 2004)

LyNx said:


> Why do you fvckers always try to work an argument to suit you instead of just stating obvious basic facts with everyone running the same, which makes everything neutral and then factor in the longer cranks or shorter cranks??
> 
> When you are honest and not trying to skew facts, you realise that if person A has 160mm cranks and is turning a 23 inch gear @ 200WATTS and person B is running 180mm cranks and turning the same 23inch gear @ same 200 WATTS, the person with the longer cranks is putting out more torque with less RPMs so the person with the shorter cranks will have them to spin faster, thereby possibly smacking one of those rocks we all encounter, thereby stalling them or making them dab, fairly fvcking simple when you're honest.


Well then, by your logic, the honest simple answer is to get 200mm cranks, spin even slower @ 200w which will decrease rock smacks even further...wait...


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## Charlie Don't Surf (Mar 31, 2017)

*OneSpeed* said:


> Maybe I shouldn't have said "most", but many shorter cranks are just re-drilled 175's.


You're good, my reply wasn't intended to be akin to 1/2 of the responses in this thread, this is just the first set I've noticed like that (and only because the crank boots came up shallow)


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## richwolf (Dec 8, 2004)

To compare an engine to human legs turning is like comparing my friends head to the man in the moon. Oh wait his head does look like that!
A longer lever is appropriate for the lower rpm of a person vs. that of an engine that turns usually over 2000 rpm and aren't trying to balance a bicycle up or down a steep inline. Or trying to avoid pedal strikes on rocks. Most people pedal at around 50 to 90 rpm so that is multitudes slower than a motor.
My take is I want something around 13 inches high on a hardtail. I tried 150 cranks for a while and they just don't give the leverage I need to climb effectively. I agree using a higher rpm can lead to more pedal strikes and at a certain steepness and length you are pretty much reduced to a low rpm. Of course longer cranks add to the equation of more pedal strikes. 
The bike industry usually goes to extremes to see what will stick or they keep re purposing the same rim, frame etc. to fit the latest trends. For example 27.5 plus bikes based on 29er frames are going to have a lower BB.
Hey if you wanna rail some turns then a lower BB might be the way to go. If you like techy uphill climbing then probably go with a higher BB.
Another thought is with a lower bottom bracket shorter cranks probably will not reduce the number of pedal strikes because most of the time you are in the pedals level position. A lower bottom bracket will reduce clearance on both sides and a shorter crank will only help part of the time. Every tenth of an inch in lower BB height will mathematically lead to more pedal strikes, more unplanned dismounts and more broken bones. (But hey don't ax me to do the math!)


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## bronxbomber252 (Mar 27, 2017)

richwolf said:


> To compare an engine to human legs turning is like comparing my friends head to the man in the moon. Oh wait his head does look like that!
> A longer lever is appropriate for the lower rpm of a person vs. that of an engine that turns usually over 2000 rpm and aren't trying to balance a bicycle up or down a steep inline. Or trying to avoid pedal strikes on rocks. Most people pedal at around 50 to 90 rpm so that is multitudes slower than a motor.
> My take is I want something around 13 inches high on a hardtail. I tried 150 cranks for a while and they just don't give the leverage I need to climb effectively. I agree using a higher rpm can lead to more pedal strikes and at a certain steepness and length you are pretty much reduced to a low rpm. Of course longer cranks add to the equation of more pedal strikes.
> The bike industry usually goes to extremes to see what will stick or they keep re purposing the same rim, frame etc. to fit the latest trends. For example 27.5 plus bikes based on 29er frames are going to have a lower BB.
> Hey if you wanna rail some turns then a lower BB might be the way to go. If you like techy uphill climbing then probably go with a higher BB.


Actually the difference between 50 and 90 RPM is great enough to justify a discussion of crank length. Since the power equation multiplies by RPM instead of adding, the difference between a rider with 50 RPM who puts a large amount of force through the pedals and one at 90 RPM that puts a little less force through the pedals is absolutely comparable to the difference between a 5000RPM V-8 with 240 hp (like a early 2000's Mustang) and a 9000RPM I-4 with 240 hp (like an early Honda S2000). In both cases, the lower RPM example has more torque and needs higher gearing/longer cranks to avoid spinning out/redlining but makes up for it with torque; and the higher RPM example uses a lower gear/shorter cranks to take advantage of the higher RPM to make power.

In the bike example, the individual rider must determine whether shorter crank to allow pedaling over stuff, or the increased torque of a longer crank and less RPM to ratchet over stuff is the better fit for their riding style and personal strengths.


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## scrublover (Dec 30, 2003)

I love how these sorts of threads always turn into some sort of d!ck measuring contest about whose trails are chunkier/uglier/rawkier than everyplace else.


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## MOJO K (Jan 26, 2007)

I didn't realize how bad new bikes suck....important consumer info here.


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## richwolf (Dec 8, 2004)

Dave Moulton has a different take on bottom bracket height. Dave Moulton's Blog - Dave Moulton's Bike Blog - Bottom Bracket Height

It is interesting to read about how BB drop affects the tubing on the rest of the frame.


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## grumpy old biker (Jul 29, 2014)

I'm trying to get some perspective to this issue you are discussing about, but never even ridden trail bike, I'm not sure how it would compare to my trusty 26er in this aspect.

Is there more than 5mm difference in BB height between 26er and modern trail bike?

I wonder how much worse it would be, pedals have seen 2 weeks of use and I started hitting cranks 3 weeks ago when finding out nice rocky trails. Of course I'm doing it wrong and that is reason why I hit so many rocks, but it would be nice to know how much difference there really is.

My cranks are 170mm, not much options to choose from when using square taper.


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## MOJO K (Jan 26, 2007)

Feeling a little less cynical now, so...

The content of this thread is interesting in that a lot of riders seem to be looking at a single aspect of the bike design in isolation from the whole and therefore coming to conclusions that aren't entirerly correct. Modern designs have shifted, taking more cues from downhill bikes. Ride a true DH bike through some true DH terrain, and you'll be banging your cranks and pedals and bashring all the time. It's not a function of how high the bottom bracket is to start, but how low it is at full compression...8 inches of travel and maybe another inch of tire compression if the front and back G-out at the same time. Now trail bikes won't experience that kind of extreme, and air suspension will ramp up at the end in a way that DH coils aren't meant to, but I have to think that guys who are experiencing way more pedal strikes than before are dealing with functions of bike design way more dynamic than the static BB height. Finding your compromise in ride height, suspension sag and ramp-up, rebound rate, and tire pressure will probably all be a bigger part of the solution than crank length.


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## singletrackmack (Oct 18, 2012)

^yup. I mentioned suspension set up earlier in the thread as this can have a huge effect on BB height. The difference in a 10% sag set up vs a 30% sag set up on modern long travel bikes can change the BB height while riding by over an inch (25mm to 30mm). 

I don't understand why there are so many focused on things like a 5mm change in crank length when a simple suspension adjustment can easily get your BB higher while riding. 

Using compression or the pedal platform will help keep the bike sitting higher in its travel keeping the Bb higher and help avoid pedal strikes. Pretty simple way to help prevent pedal strikes.

Also, I wonder if the wide rim/ big tire/ low tire pressure trend is playing into causing the Bb to sit lower when riding through chunk. With static bb height being set with big tires at PSI higher than one would normally ride, that means that there is more Bb drop Is even more than before when the tire compresses.


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## Sideknob (Jul 14, 2005)

singletrackmack said:


> ^yup. I mentioned suspension set up earlier in the thread as this can have a huge effect on BB height. The difference in a 10% sag set up vs a 30% sag set up on modern long travel bikes can change the BB height while riding by over an inch (25mm to 30mm).
> .


And in all likelihood mean the 150mm AM bike you want becomes a heavy 100mm travel bike...etc


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## MOJO K (Jan 26, 2007)

Sideknob said:


> And in all likelihood mean the 150mm AM bike you want becomes a heavy 100mm travel bike...etc


True. The solution has to be a combo of a little less sag, and a little quicker rebound, and enough ramp-up to keep suspension performing well while not wallowing in the bottom half of it's travel. The fact we get volume spacer tokens included to tune our stuff is a real game changer that doesn't get talked about nearly enough. Some of us used to add a couple of CCs of oil to the air shock through the air valve to get the ramp-up/ bottom out control without mucking up proper sag and small bump performance.


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## Smithhammer (Jul 18, 2015)

singletrackmack said:


> I don't understand why there are so many focused on things like a 5mm change in crank length when a simple suspension adjustment can easily get your BB higher while riding.


Cuz I actually want to use the full travel of the shock, and not have it feel like a basketball in the lower part of the stroke?

But I get your point, and it's certainly a valid one - _some_ of the issue can be addressed with sus setup, at least.


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## Sideknob (Jul 14, 2005)

MOJO K said:


> True. The solution has to be a combo of a little less sag, and a little quicker rebound, and enough ramp-up to keep suspension performing well while not wallowing in the bottom half of it's travel. The fact we get volume spacer tokens included to tune our stuff is a real game changer that doesn't get talked about nearly enough. Some of us used to add a couple of CCs of oil to the air shock through the air valve to get the ramp-up/ bottom out control without mucking up proper sag and small bump performance.


Yeah, I remember doing that right back in the mid 90's, and blending oil weights. 😁


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## scrublover (Dec 30, 2003)

mojo k said:


> the solution has to be a combo of a little less sag, and a little quicker rebound, and enough ramp-up to keep suspension performing well while not wallowing in the bottom half of it's travel. And learning to pedal your f*cking bicycle.


ftfy.


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## scrublover (Dec 30, 2003)

Dave Moulton is a genius in some aspects of bike design.

Modern full suspension mtb design...yeah...um...no.


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## MOJO K (Jan 26, 2007)

scrublover said:


> ftfy.


Thanks, Dave...You still in CT?


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## Sideknob (Jul 14, 2005)

So....I can pump my shock and fork up hard, drop back to 160mm cranks and I'm good to go?

Cool! 

Sounds like heaven on the chunky ups and downs.


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## singletrackmack (Oct 18, 2012)

Smithhammer said:


> Cuz I actually want to use the full travel of the shock, and not have it feel like a basketball in the lower part of the stroke?
> 
> But I get your point, and it's certainly a valid one - _some_ of the issue can be addressed with sus setup, at least.


If your looking to either get new cranks and go from 175 to 170, I think increasing the sag a few % is worth a try first.

Going from 30% sag on a 150mm FS, to 27% sag should raise the BB while riding by about 5mm. Maybe turn the compression up a notch or two as well and get the riding height a little higher and keep the longer cranks.



Sideknob said:


> So....I can pump my shock and fork up hard, drop back to 160mm cranks and I'm good to go?
> 
> Cool!
> 
> Sounds like heaven on the chunky ups and downs.


What kinda of BB height increase needed on modern bikes are we talking about?

Are the BBs 10mm too low, 25mm too low or what?


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## richwolf (Dec 8, 2004)

I don't think the average mountain biker is going to go through a lot of gyrations to check their shocks or modify them like many of you do. 
Tire pressure, most don't check every ride or pump them up too hard.
Shock pressure, how many people check on a regular basis or make sure the have the right amount of sag?
Shifting system, how many people have crappy shifting bikes due to lack of maintenance or knowledge on how to fix them? Dirty cables? Hey I just changed them last year!

All this talk about crank length is ignoring the fact that given a certain bottom bracket height, all length cranks are going to be the same distance off the ground when you are in a pedals neutral position. How many of these rock slams and dismounts come when you are in this position? Plenty if not most in my opinion.
A shorter crank will definitely give more strikes when you are pedaling but a lower bottom bracket regardless of crank length will lead to more pedal strikes than a bike with a higher bottom bracket.
Long low and slack is the new buzzword but it ain't the recipe for everyone or every trail. How about long, high and slack? Also these travel wars are going to lead to more pedal strikes too.


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## Smithhammer (Jul 18, 2015)

singletrackmack said:


> If your looking to either get new cranks and go from 175 to 170, I think increasing the sag a few % is worth a try first.
> 
> Going from 30% sag on a 150mm FS, to 27% sag should raise the BB while riding by about 5mm. Maybe turn the compression up a notch or two as well and get the riding height a little higher and keep the longer cranks.


Thanks, but I went to 170 cranks for multiple reasons. I just also happened to notice fewer pedals strikes as a result.



richwolf said:


> I don't think the average mountain biker is going to go through a lot of gyrations to check their shocks or modify them like many of you do.
> Tire pressure, most don't check every ride or pump them up too hard.
> Shock pressure, how many people check on a regular basis or make sure the have the right amount of sag?
> Shifting system, how many people have crappy shifting bikes due to lack of maintenance or knowledge on how to fix them? Dirty cables? Hey I just changed them last year!


Well, if someone isn't going to bother doing those things, then it's hard to have any sympathy for them when things aren't working the way they want them to. Not sure what else to say about that.



richwolf said:


> All this talk about crank length is ignoring the fact that given a certain bottom bracket height, all length cranks are going to be the same distance off the ground when you are in a pedals neutral position. How many of these rock slams and dismounts come when you are in this position? Plenty if not most in my opinion.
> A shorter crank will definitely give more strikes when you are pedaling but a lower bottom bracket regardless of crank length will lead to more pedal strikes than a bike with a higher bottom bracket.
> Long low and slack is the new buzzword but it ain't the recipe for everyone or every trail. How about long, high and slack? Also these travel wars are going to lead to more pedal strikes too.


Obviously, if you are someone who has an issue with pedal strikes (which may or may not be the result of BB height), and you are looking for a _new_ bike, then seek out a frame that has a higher BB, among other things. Shorter cranks, thinner pedals, along with other suggestions in this thread, are for people who would like to try and address these issues on bikes they _already_ own.


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## evasive (Feb 18, 2005)

richwolf said:


> All this talk about crank length is ignoring the fact that given a certain bottom bracket height, all length cranks are going to be the same distance off the ground when you are in a pedals neutral position. How many of these rock slams and dismounts come when you are in this position? Plenty if not most in my opinion.


My experience is the opposite. I rarely hit a pedal in that position.


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## richwolf (Dec 8, 2004)

Smithhammer said:


> Thanks, but I went to 170 cranks for multiple reasons. I just also happened to notice fewer pedals strikes as a result.
> 
> Well, if someone isn't going to bother doing those things, then it's hard to have any sympathy for them when things aren't working the way they want them to. Not sure what else to say about that.
> 
> Obviously, if you are someone who has an issue with pedal strikes (which may or may not be the result of BB height), and you are looking for a _new_ bike, then seek out a frame that has a higher BB, among other things. Shorter cranks, thinner pedals, along with other suggestions in this thread, are for people who would like to try and address these issues on bikes they _already_ own.


Don't have an issue with them because I picked the right bottom bracket height and ride a hardtail. Seems funny though that we are seeing more and more discussion about BB strikes
Thinner pedals, and shorter cranks to me are a band-aide that shouldn't be part of the equation in making a bike work. I don't want to give up my longer levers for uphill efforts. Sure you can supposedly spin faster but the human body is not a motor and after a while you run out of low gear and energy to where a longer crank just plain works better.
New bikes with low BB's, lots of travel and one by systems that for many don't give enough gear range is the new breed but it ain't the best for many of us. But hey if 150 cranks, slim pedals and having no sag work for you then more power to you!


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## richwolf (Dec 8, 2004)

evasive said:


> My experience is the opposite. I rarely hit a pedal in that position.


But when you hit it in that position it most likely will launch you. Has happened to many of my friends. A low bottom bracket with a neutral pedal position is going to ride closer to the ground and features than a higher one in the neutral position. That well grounded rock that you cleared by just 1/4 to 1/2 inch is now firmly in pedal strike territory. 
But if your are happy with your bike and how it handles then you made the right choice. Just won't be a choice that I am making!
I bought a plus bike hardtail with 27.5 plus tires which was basically a 29er with different wheels and tires that lowered the BB. I noticed a lot more pedal strikes than with my old 29er. When I shopped for a 29 plus bike that was one of my criteria was to have a bike with a higher BB. I think what little stability you get from having your mass a little bit lower is not worth it to me. Perhaps the "new geometry" bike's stability has more to do with long and slack and dropper posts (not to mention the baggy shorts!)
And just cause a manufacturer says long low and slack might mean they are using a frame (designed around a larger diameter wheel) with a smaller diameter wheel and using spin to market it.


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## RadBartTaylor (Dec 1, 2004)

richwolf said:


> But when you hit it in that position it most likely will launch you. Has happened to many of my friends. A low bottom bracket with a neutral pedal position is going to ride closer to the ground and features than a higher one in the neutral position. That well grounded rock that you cleared by just 1/4 to 1/2 inch is now firmly in pedal strike territory.
> But if your are happy with your bike and how it handles then you made the right choice. Just won't be a choice that I am making!
> I bought a plus bike hardtail with 27.5 plus tires which was basically a 29er with different wheels and tires that lowered the BB. I noticed a lot more pedal strikes than with my old 29er. When I shopped for a 29 plus bike that was one of my criteria was to have a bike with a higher BB. I think what little stability you get from having your mass a little bit lower is not worth it to me. Perhaps the "new geometry" bike's stability has more to do with long and slack and dropper posts (not to mention the baggy shorts!)
> And just cause a manufacturer says long low and slack might mean they are using a frame (designed around a larger diameter wheel) with a smaller diameter wheel and using spin to market it.


How high is your BB on your current bike and what is the BB drop?


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## richwolf (Dec 8, 2004)

ArizRider said:


> How high is your BB on your current bike and what is the BB drop?


It's a secret!


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## richwolf (Dec 8, 2004)

Actually a Trek Stache 5 with a 120 Manitou front fork. 
I think I remember it was a shade under 13 inches before fork sag and tire sag. It is lower now with the 2.6 Nobby Nics on it, and I do notice the difference with a few more rock strikes that I didn't get with the 3.0 inch tires on it, but it certainly is not a huge concern. I don't notice any difference in my ability "to rail the turns"
I think my first plus bike was around 12 inches or so.
It would be interesting to take a "new geometry bike" and raise the BB just to see what the difference was in "railing turns" (of course with baggies on!)


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## Smithhammer (Jul 18, 2015)

richwolf said:


> ....I don't want to give up my longer levers for uphill efforts. Sure you can supposedly spin faster but the human body is not a motor and after a while you run out of low gear and energy to where a longer crank just plain works better....


Like you said, if that's what works for you great. But it's been amply demonstrated that there is a lot more to the equation than simply, "longer lever = better."

My current full sus bike has a 13.1" BB. A little lower than I'd like it in a perfect world, but slightly shorter cranks, thinner pedals and adjusting my technique a bit have largely addressed that. And the latter in particular is making me a better rider in the techie spots.


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## Charlie Don't Surf (Mar 31, 2017)

I'll try to measure my Stache 9 with 140mm fork and 27.5 2.8 Nobby Nics tonight, think it's right around 12"


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## RadBartTaylor (Dec 1, 2004)

richwolf said:


> But when you hit it in that position it most likely will launch you. Has happened to many of my friends. A low bottom bracket with a neutral pedal position is going to ride closer to the ground and features than a higher one in the neutral position. That well grounded rock that you cleared by just 1/4 to 1/2 inch is now firmly in pedal strike territory.
> But if your are happy with your bike and how it handles then you made the right choice. Just won't be a choice that I am making!
> I bought a plus bike hardtail with 27.5 plus tires which was basically a 29er with different wheels and tires that lowered the BB. I noticed a lot more pedal strikes than with my old 29er. When I shopped for a 29 plus bike that was one of my criteria was to have a bike with a higher BB. I think what little stability you get from having your mass a little bit lower is not worth it to me. Perhaps the "new geometry" bike's stability has more to do with long and slack and dropper posts (not to mention the baggy shorts!)
> And just cause a manufacturer says long low and slack might mean they are using a frame (designed around a larger diameter wheel) with a smaller diameter wheel and using spin to market it.


Remember than running a double (like you prefer) lowers your effective clearance over a single ring, substantially. If your going to hit something with level pedals (I don't) your going to hit your chain/chainring.

If we assume a 24/36 ring vs a 30 single, it's about 1" difference in diameter or 1/2" difference in clearance....to your point of 1/4" to 1/2" making a difference, there you have it.


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## richwolf (Dec 8, 2004)

Smithhammer said:


> Like you said, if that's what works for you great. But it's been amply demonstrated that there is a lot more to the equation than simply, "longer lever = better."
> 
> My current full sus bike has a 13.1" BB. A little lower than I'd like it in a perfect world, but slightly shorter cranks, thinner pedals and adjusting my technique a bit have largely addressed that. And the latter in particular is making me a better rider in the techie spots.


Glad it is working for you and making you a better rider.
When I got my last bike I didn't want to fiddle with a bunch of changes just to address the issues of a low BB. I sacrificed some "railability" to reduce pedal strikes!
And this old dog ain't willing or able to change my technique much.


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## richwolf (Dec 8, 2004)

ArizRider said:


> Remember than running a double (like you prefer) lowers your effective clearance over a single ring, substantially. If your going to hit something with level pedals (I don't) your going to hit your chain/chainring.
> 
> If we assume a 24/36 ring vs a 30 single, it's about 1" difference in diameter or 1/2" difference in clearance....to your point of 1/4" to 1/2" making a difference, there you have it.


32-22 is my double. Also my chainrings don't stick out as far as my pedals do. I think with platform pedals (which I happen to run) you are going to get more pedal strikes.
What size is your ring and do we now suggest that people with low bottom brackets go with smaller rings? Plus I see a lot more marks from hitting things on pedals than on chain rings. There you have it!
Plus baggies run low and take up more width than lycra so you get more strikes right there!


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## RadBartTaylor (Dec 1, 2004)

richwolf said:


> 32-22 is my double. Also my chainrings don't stick out as far as my pedals do. I think with platform pedals (which I happen to run) you are going to get more pedal strikes.
> What size is your ring and do we now suggest that people with low bottom brackets go with smaller rings? Plus I see a lot more marks from hitting things on pedals than on chain rings. There you have it!
> Plus baggies run low and take up more width than lycra so you get more strikes right there!


So you like really low gears, we can use a 28t single ring to compare which is still 1/4" higher than the double setup, and per your comment, 1/4" matters.

When your pedals are horizontal, I still don't understand how you could hit em with any significant impact.


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## grumpy old biker (Jul 29, 2014)

ArizRider said:


> So you like really low gears, we can use a 28t single ring to compare which is still 1/4" higher than the double setup, and per your comment, 1/4" matters.
> 
> When your pedals are horizontal, I still don't understand how you could hit em with any significant impact.


I believe that is to do with horizontal dimension, pedals are some 2 inch or maybe more to right and left of the crank and if you clip rock too sharp it is pedal that hits, not so much the crank itself.

That probably classifies as a rider error though, but then again aren't most pedal/crank strikes rider errors, you have your tool and you have to use it way it works best, some tools are harder than others.

I know I'm bit too enthusiast with rocks, 44T starts to have few trimmed teeth, need new pedals soon, but there is nothing like a fresh smell of aluminum at the morning rocks.

According to map this descent varies between 25% to 45% might need few attempts before try at the speed. 









I think you can get pedal strikes at any position at some of the rocks along that trail as there are boulders and you have to go trough narrow gaps between them etc.










Then it comes to how much technical and how much speed, strikes at technical terrain or slow speed are not much of the bother really, at least for me. 
Going faster and it of course becomes increasingly difficult to hit pedals at vertical, crank strikes becoming indeed quite impossible.

Can we just say it's not the bike, it's the rider?


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## RAKC Ind (Jan 27, 2017)

Quite true, it is always the rider. They dont choose a bike for their terrain then blame the bikes for not learning all aspects of said bike.

Now its true, lower BBs are very much a thing. And regardless of the debate, there is no arguing physics, lower the COG and handling changes. Faster speeds while turning, more "in" instead of "on top of" the bike.

For most they are a problem because the lower bb has decreased margin of error allowed and made some terrain increasingly difficult to ride.

It all comes down to the rider no matter what though. Rider chose the bike. I have noticed the negative side of lower BB, never a bad crash because of it though. Had more issues with a bike that had more clearance. The lower CG along with current geo has made it easier to recover from such a strike.

No sure HOW but no real crash on this bike yet. Toes in pain more than once, had to drop a foot a couple times to avoid falling over, but unlike before I have stayed on the bike and recovered from each incident. Yes its a combo of new geometry, which includes the lower COG due to lower BB. 

It can be learned and adapted to if the benefits outweigh the drawbacks for the rider. But THE RIDER has to make that determination and make educated choices on which bike they choose.

Sent from my SM-G950U using Tapatalk


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## prj71 (Dec 29, 2014)

RAKC Ind said:


> lower the COG and handling changes. Faster speeds while turning, more "in" instead of "on top of" the bike.


COG is about a 4ft or more off the ground when your riding a bike. Because its so far off the ground, lowering the BB has little to no effect on stability when the center of mass is so high. If someone wipes it's from leaning too far into a corner, or sliding out on a rock, gravel, wet root etc.

However a 325mm vs. 335mm BB height (about 3/8") does make the difference in pedal striking or not pedal striking.

It's easier and makes more sense to purchase a bike with a higher BB than saying...well you just need to adjust your pedaling motions.


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## richwolf (Dec 8, 2004)

prj71 said:


> COG is about a 4ft or more off the ground when your riding a bike. Because its so far off the ground, lowering the BB has little to no effect on stability when the center of mass is so high. If someone wipes it's from leaning too far into a corner, or sliding out on a rock, gravel, wet root etc.
> 
> However a 325mm vs. 335mm BB height (about 3/8") does make the difference in pedal striking or not pedal striking.
> 
> It's easier and makes more sense to purchase a bike with a higher BB than saying...well you just need to adjust your pedaling motions.


No you got it all wrong, it is the chainrings that are the problem!


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## RadBartTaylor (Dec 1, 2004)

richwolf said:


> No you got it all wrong, it is the chainrings that are the problem!


Lets be fair here - YOU were the one saying 1/2" to 1/4" was all the difference, not anybody else, was just pointing to the fact that you could give yourself an edge by running a 1x....based on your logic.


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## Thustlewhumber (Nov 25, 2011)

prj71 said:


> COG is about a 4ft or more off the ground when your riding a bike. Because its so far off the ground, lowering the BB has little to no effect on stability when the center of mass is so high.


What


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## grumpy old biker (Jul 29, 2014)

Where COG is when you lift your butt 1/2" off from the saddle and weight is at pedals more than on saddle?


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## richwolf (Dec 8, 2004)

here is a picture with bicycle forces including center of gravity


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## grumpy old biker (Jul 29, 2014)

richwolf said:


> here is a picture with bicycle forces including center of gravity
> View attachment 1165102


I think that it is bit more complex than that, pivot at seat or pivot at BB changes how bike handles, we all lift our butt from saddle when we need bike to handle, well, at least we who ride HT do that, never had chance to ride FS, those might work bit differently.

With all MTBs rider moves around a lot changing position of COG to make bike do things rider wants to, there is very unlikely static COG or even COG height.

Road cycling might differ here as cornering is done seated in those. Faster I go, less I sit on saddle, when riding a horse and doing a jump, sitting is sure way to land nose first to ground, I treat dirt bikes and mountain bikes same way.

There probably is proper science about this that tackles MTB specific aspects properly, but it is likely far more complex than static cornering.


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## richwolf (Dec 8, 2004)

grumpy old biker said:


> I think that it is bit more complex than that, pivot at seat or pivot at BB changes how bike handles, we all lift our butt from saddle when we need bike to handle, well, at least we who ride HT do that, never had chance to ride FS, those might work bit differently.
> 
> With all MTBs rider moves around a lot changing position of COG to make bike do things rider wants to, there is very unlikely static COG or even COG height.
> 
> ...


Even if you are standing on the pedals the COG is not at the pedals it is well above the pedals. Dropper posts allow you to lower your COG by moving your mass down. 
If you can find some info that proves otherwise I would like to see it.


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## richwolf (Dec 8, 2004)

Center of mass of a standing individual. Of course it will change by body position. But even crouched over a bicycle it will probably be near or over the top tube.


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## bronxbomber252 (Mar 27, 2017)

Given the weight if bikes relative to humans (1/8-1/5), and where most humans weight sits, the overall COG will usually be in the general vicinity of the riders hips regardless of whether the rider puts weight on the pedals, saddle, or handlebars.


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## richwolf (Dec 8, 2004)

bottom bracket heights 

Wife's airborne Griffin with specialized purgatory 27.5 by 3 inch tires 11 7/8 inches 

Ti HT 29 by 2.35 tires 12 1/2 inches 

Trek stache 29 by 2.6 inch tires
12 3/8 inches 
Of course the stache BB is higher 👆 with 3.0 tires on it


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## Charlie Don't Surf (Mar 31, 2017)

richwolf said:


> bottom bracket heights
> 
> Wife's airborne Griffin with specialized purgatory 27.5 by 3 inch tires 11 7/8 inches
> 
> ...


 By comparison... Airborne Griffin 140mm fork 25% sag,27.5+ DT Swiss XM521 35mm ID rims with Schwalabe Nobby Nic 2.8 tires 11.60", Trek Stache 9 with 120mm fork at 20% sag, 29 + Easton ARC 40 ID with Schwalabe 2.6 Nobby Nic 12.4", with 140mm fork and DT 27.5+ combo 11.35".


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## Fajita Dave (Mar 22, 2012)

bronxbomber252 said:


> Given the weight if bikes relative to humans (1/8-1/5), and where most humans weight sits, the overall COG will usually be in the general vicinity of the riders hips regardless of whether the rider puts weight on the pedals, saddle, or handlebars.


Standing or sitting doesn't change the COG much at all but it does dramatically change the moment of inertia.

A lower MOI will give the bike a much more lively ride. Try a quick swerve while sitting then try it again with your body weight on the pedals.


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## Cornfield (Apr 15, 2012)

Why is it called a Bottom Bracket if there's no Top Bracket?


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## Cleared2land (Aug 31, 2012)

Entertain the theoretical.


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## bronxbomber252 (Mar 27, 2017)

Fajita Dave said:


> Standing or sitting doesn't change the COG much at all but it does dramatically change the moment of inertia.
> 
> A lower MOI will give the bike a much more lively ride. Try a quick swerve while sitting then try it again with your body weight on the pedals.


If you want to get real technical, with regard to lean, it is only changing how much of the mass is moved (leaned) since you are leaning the bike under you for properly cornering while standing, the axis of rotation is still where the tires meet the ground, and the mass is still in a similar spot. By contrast leaning with the bike while seated has the mass move further. In essence you are changing the effective MOI of the bike itself without changing the actual MOI if the entire system very much.

With regard to the direction change, the axis of rotation is at a theoretical spot that you would make a circle around if you maintained the turn for 360 degrees. Since the distance to the axis of rotation is large enough that moving your body around makes little difference, what you are trying to do is make sure that the sum force vector goes through the tire and into the ground. Thus you move your CoG toward the inside of the turn.

The liveliness you describe is mostly the rate at which you can change the lean angle of the bike which is why standing up and leaning the bike under you makes it so. Additionally some of that perceived liveliness comes from a combo increased grip of positioning your CoG in line with the average force vector, and the way MTB tires are designed with bigger cornering knobs on the edges making leaning the bike further than the rider very helpful.


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## Grassington (Jun 24, 2017)

^ Leaning the bike more also reduces the cornering radius, which means you don't have to turn the front wheel so much, which means the front tyre doesn't scrub as much, which means you go faster! Here's a question then, and a shiny new rep point to the first person who can give me the correct answer: I can take a corner - even at low speeds - by leaning my body more than my bike, a bit like a racing motorcycle on a high speed bend. How do I manage this without falling over?

As for low BBs, yeah, I'm not a fan. I never had any issues with the old BB heights, didn't have so many damn pedal strikes either. Had a pedal strike on the flat the other day. OK, it was flat made up from fist-sized hardcore, but still...


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## alexbn921 (Mar 31, 2009)

All 2 wheel vehicles rotate around the COG just like an airplane. Tire contact point has very little influence on that point.


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## alexbn921 (Mar 31, 2009)

Grassington said:


> ^ Leaning the bike more also reduces the cornering radius, which means you don't have to turn the front wheel so much, which means the front tyre doesn't scrub as much, which means you go faster! Here's a question then, and a shiny new rep point to the first person who can give me the correct answer: I can take a corner - even at low speeds - by leaning my body more than my bike, a bit like a racing motorcycle on a high speed bend. How do I manage this without falling over?


Leaning the bike doesn't change change the cornering radius. Only your center of gravity changes your cornering radius. Leaning your body out and keeping the bike more upright doesn't engage the soft side lugs. Leaning your bike more and keeping your body more upright gives an identical COG and you are in a better body position to respond to changes in traction.


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## richwolf (Dec 8, 2004)

MOI???

With low bottom brackets sometimes the "moment of inertia" becomes the "moment of impact"!!


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## richwolf (Dec 8, 2004)

A little video on head angle and BB height. Why do they always sound like they are talking with a sammich in their mouth?!





I do wonder really how much a lower bottom bracket makes a bike handle better? Might it not be more a function of a slacker head angle, longer top tube, wider tires and perhaps chainstay length?
The reason I ask this is because my Stache seems to handle no differently with 2.6 inch tires vs. 3.0 inch tires where my BB is changed by almost 1/2 inch. In fact it handles better with the bigger tires.
We have ascertained that the COG of rider and bike is several feet off the ground so I don't see how a 1/2 inch to 1 inch higher BB is going to change the handling that much?
And with the suspension travel wars in full on mode you are going to need a higher BB.


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## Fajita Dave (Mar 22, 2012)

bronxbomber252 said:


> If you want to get real technical, with regard to lean, it is only changing how much of the mass is moved (leaned) since you are leaning the bike under you for properly cornering while standing, the axis of rotation is still where the tires meet the ground, and the mass is still in a similar spot. By contrast leaning with the bike while seated has the mass move further. In essence you are changing the effective MOI of the bike itself without changing the actual MOI if the entire system very much.
> 
> With regard to the direction change, the axis of rotation is at a theoretical spot that you would make a circle around if you maintained the turn for 360 degrees. Since the distance to the axis of rotation is large enough that moving your body around makes little difference, what you are trying to do is make sure that the sum force vector goes through the tire and into the ground. Thus you move your CoG toward the inside of the turn.
> 
> The liveliness you describe is mostly the rate at which you can change the lean angle of the bike which is why standing up and leaning the bike under you makes it so. Additionally some of that perceived liveliness comes from a combo increased grip of positioning your CoG in line with the average force vector, and the way MTB tires are designed with bigger cornering knobs on the edges making leaning the bike further than the rider very helpful.


I agree 

A lower MOI where you're in contact with the bike wont have any effect on cornering grip. It will allow the bike to respond much quicker which is also the goal with the new shorter chain stays. Having both makes a bike thats much more playful to ride. I doubt it would let anyone actually ride faster but that responsive ride could boost confidence. Its sure as hell a lot more fun.

Cornering radius is all about how far you can move the bike/rider COG into the corner. The more the COG moves left or right of the tire tracks the sharper the bike needs to turn to avoid falling over. Lean angle is only a product of equalibrium between cornering force and gravity pulling you to the ground. A lower BB wont help at all here.

Edit: The GMBN video above is completely wrong when they get to the BB height. Lowering a BB by an inch or so has practically no effect on your COG and cornering.


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## Grassington (Jun 24, 2017)

alexbn921 said:


> Leaning the bike doesn't change change the cornering radius. Only your center of gravity changes your cornering radius. Leaning your body out and keeping the bike more upright doesn't engage the soft side lugs. Leaning your bike more and keeping your body more upright gives an identical COG and you are in a better body position to respond to changes in traction.


Nope, leaning the bike does indeed reduce the cornering radius. Maths at https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics, "(the) lean of the bike decreases the actual radius of the turn proportionally to the cosine of the lean angle." Other variables are steering angle, wheelbase and caster angle. CoG doesn't come into turn radius, excepting that moving your CoG about can enable you to lean the bike at different angles.

C'mon bicycle dynamics experts: how can I lean my body more than my bike in low speed corners and not fall off? Rep point not enough, do I have to offer a cash prize?


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## alexbn921 (Mar 31, 2009)

Grassington said:


> Nope, leaning the bike does indeed reduce the cornering radius. Maths at https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics, "(the) lean of the bike decreases the actual radius of the turn proportionally to the cosine of the lean angle." Other variables are steering angle, wheelbase and caster angle. CoG doesn't come into turn radius, excepting that moving your CoG about can enable you to lean the bike at different angles.
> 
> C'mon bicycle dynamics experts: how can I lean my body more than my bike in low speed corners and not fall off? Rep point not enough, do I have to offer a cash prize?


You math is wrong. The lean angle of the COG is the important point. Actual lean angle of the bike is irrelevant.
You can lean your bike way over and counter with you body and you will go strait because your COG is directly over the contact patch.
Steering angle at speed is only used to influence your COG. If you turn into a turn you imitate a change of direction. Your steady state radius is only effected by your COG distance from the contact patch.


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## bronxbomber252 (Mar 27, 2017)

Fajita Dave said:


> I agree
> 
> A lower MOI where you're in contact with the bike wont have any effect on cornering grip. It will allow the bike to respond much quicker which is also the goal with the new shorter chain stays. Having both makes a bike thats much more playful to ride. I doubt it would let anyone actually ride faster but that responsive ride could boost confidence. Its sure as hell a lot more fun.
> 
> ...


True MOI is based soley on the location of the mass (all of it, not just COG) relative to the axis of rotation. not the point at which the the force is applied. The reason you have a better MOI while standing is not because the weight is pushing on the pedals, but rather, because you can lean better thus moving your COG and MOI closer to the inside of the corner. The reason you can lean faster is because you can move the bike under your body without moving your body thus removing much of your body from the MOI equation for the leaning of the bike.


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## Fajita Dave (Mar 22, 2012)

Grassington said:


> C'mon bicycle dynamics experts: how can I lean my body more than my bike in low speed corners and not fall off? Rep point not enough, do I have to offer a cash prize?


Not that I care about a rep point. The bike vs body lean is pretty irrelevant to cornering especially at low speeds. The effective lean angle of the bike/rider system is only a product of the cornering force and gravity trying to pull the COG to the ground. The bike could be leaning left and you could still be turning right. The geometry built into our bikes keeps the front wheel pointing in the direction needed to achieve balance until the rider makes an input. Once the rider makes a steering input the COG will be moved (thanks to inertia) and a different equilibrium will need to be found to provide stability.


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## Fajita Dave (Mar 22, 2012)

bronxbomber252 said:


> The reason you can lean faster is because you can move the bike under your body without moving your body thus removing much of your body from the MOI equation for the leaning of the bike.


Thats exactly what I said. The dynamics of how a bicycle and rider work together and seperately are way to complicated without writing a book about it. So I stuck with how changing the MOI of the bike will effect how it rides.

A lower BB while standing on the pedals will allow the bike to respond quicker to cornering and lean angle changes. I have no idea how much of a difference an inch or so makes with modern geo. Theres definitely other factors involved.


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## tealy (Mar 7, 2013)

okay


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## Grassington (Jun 24, 2017)

alexbn921 said:


> You math is wrong. The lean angle of the COG is the important point. Actual lean angle of the bike is irrelevant.
> You can lean your bike way over and counter with you body and you will go strait because your COG is directly over the contact patch.
> Steering angle at speed is only used to influence your COG. If you turn into a turn you imitate a change of direction. Your steady state radius is only effected by your COG distance from the contact patch.


You'll have to take the math point up with the Wikipedia page I cribbed it from. The equation they give has a 2% margin of error, so there are other forces at play too. I reckon you're avoiding my question  - given that accepted wisdom has it that the resultant force vector between the downwards gravity force through the combined CoG and the sideways centripetal force has to be a straight line that passes through both the CoG and the tyre contact patch, I'm saying that I can corner in a stable fashion with the resultant force vector _inside_ the tyre contact point. How? Clue: it's nothing to do with CoG, except that I've positioned the overall CoG in such a way that I would normally fall to the inside, except that I don't.



Fajita Dave said:


> Not that I care about a rep point. The bike vs body lean is pretty irrelevant to cornering especially at low speeds. The effective lean angle of the bike/rider system is only a product of the cornering force and gravity trying to pull the COG to the ground. The bike could be leaning left and you could still be turning right. The geometry built into our bikes keeps the front wheel pointing in the direction needed to achieve balance until the rider makes an input. Once the rider makes a steering input the COG will be moved (thanks to inertia) and a different equilibrium will need to be found to provide stability.


There's a hint to the correct answer in what you've said, but otherwise no. Also please don't lean left and turn right*, you will fall over. To the left.

* I might be splitting hairs here: by right I mean steering angle right of dead centre. You can certainly lean to the left and turn a little rightwards as long as you don't cross the dead centre position and adjust other factors to compensate.


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## bronxbomber252 (Mar 27, 2017)

Fajita Dave said:


> Thats exactly what I said. The dynamics of how a bicycle and rider work together and seperately are way to complicated without writing a book about it. So I stuck with how changing the MOI of the bike will effect how it rides.
> 
> A lower BB while standing on the pedals will allow the bike to respond quicker to cornering and lean angle changes. I have no idea how much of a difference an inch or so makes with modern geo. Theres definitely other factors involved.


Got it! We are now on the same page.


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## Fajita Dave (Mar 22, 2012)

Grassington said:


> You'll have to take the math point up with the Wikipedia page I cribbed it from. The equation they give has a 2% margin of error, so there are other forces at play too. I reckon you're avoiding my question  - given that accepted wisdom has it that the resultant force vector between the downwards gravity force through the combined CoG and the sideways centripetal force has to be a straight line that passes through both the CoG and the tyre contact patch, I'm saying that I can corner in a stable fashion with the resultant force vector _inside_ the tyre contact point. How? Clue: it's nothing to do with CoG, except that I've positioned the overall CoG in such a way that I would normally fall to the inside, except that I don't.
> 
> There's a hint to the correct answer in what you've said, but otherwise no. Also please don't lean left and turn right*, you will fall over. To the left.
> 
> * I might be splitting hairs here: by right I mean steering angle right of dead centre. You can certainly lean to the left and turn a little rightwards as long as you don't cross the dead centre position and adjust other factors to compensate.


I didn't say the front wheel would be pointing left. I said you can still be turning right with the bike leaned left. You only need your body weight to be further right than the tire contact patch . The front wheel will be pointing where ever it needs to be in order to remain upright.

Not to sound arrogent but there is nothing wrong in my last post. Everything Alex said is correct too.


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## Grassington (Jun 24, 2017)

Fajita Dave said:


> I didn't say the front wheel would be pointing left. I said you can still be turning right with the bike leaned left. You only need your body weight to be further right than the tire contact patch . The front wheel will be pointing where ever it needs to be in order to remain upright.
> 
> Not to sound arrogent but there is nothing wrong in my last post.


Yeah, I reckon that would work. I'm not going to try it because I'm old and it would probably put my back out, but the Newtonian physics is sound.

You're also close to the answer to how I can corner in a stable fashion with the resultant force of the gravity and centripetal components passing through the ground at a point to the inside of the tyre* contact patch...

* I know there's two tyres, but let's assume a single contact patch for simplicity. Usually for stability this resultant force needs to pass directly through both the contact patch and the combined CoG.


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## alexbn921 (Mar 31, 2009)

Grassington said:


> You'll have to take the math point up with the Wikipedia page I cribbed it from. The equation they give has a 2% margin of error, so there are other forces at play too. I reckon you're avoiding my question  - given that accepted wisdom has it that the resultant force vector between the downwards gravity force through the combined CoG and the sideways centripetal force has to be a straight line that passes through both the CoG and the tyre contact patch, I'm saying that I can corner in a stable fashion with the resultant force vector _inside_ the tyre contact point. How? Clue: it's nothing to do with CoG, except that I've positioned the overall CoG in such a way that I would normally fall to the inside, except that I don't.


Your talking about 2 different things now. The radius of a turn is determined by how far your COG is outside your tire contact patch. This has nothing to do with how far the bike is leaned. Also bikes don't pivot around the tires, the pivot around the COG. This is the reason that all 2 wheeled vehicles have to counter steer to initiate a turn at speed.

For the bike to be balanced in a turn, not falling in or raising up then yes centripetal force will counter act gravity and your COG vector will be perfectly inline with the tires contact patch. If you change this relationship you will not be in a steady state.











Grassington said:


> There's a hint to the correct answer in what you've said, but otherwise no. Also please don't lean left and turn right*, you will fall over. To the left.
> 
> * I might be splitting hairs here: by right I mean steering angle right of dead centre. You can certainly lean to the left and turn a little rightwards as long as you don't cross the dead centre position and adjust other factors to compensate.


You can basically lay your bike over on it's side and continue in a straight line as long as your COG is over the contact patch.


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## Fajita Dave (Mar 22, 2012)

Grassington said:


> * I know there's two tyres, but let's assume a single contact patch for simplicity. Usually for stability this resultant force needs to pass directly through both the contact patch and the combined CoG.


This makes it sound like you're talking about camber thrust but your original challenge was about leaning your body while keeping the bike upright. So camber thrust wouldn't be a factor.


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## Grassington (Jun 24, 2017)

alexbn921 said:


> Your talking about 2 different things now. The radius of a turn is determined by how far your COG is outside your tire contact patch. This has nothing to do with how far the bike is leaned. Also bikes don't pivot around the tires, the pivot around the COG. This is the reason that all 2 wheeled vehicles have to counter steer to initiate a turn at speed.
> 
> For the bike to be balanced in a turn, not falling in or raising up then yes centripetal force will counter act gravity and your COG vector will be perfectly inline with the tires contact patch. If you change this relationship you will not be in a steady state.
> 
> ...


The radius of the turn is determined by several factors, and the lean angle of the actual bike is one of them. It's not dominant, but it can be significant. There are more forces in play during cornering than just gravity and the centripetal force, and it's possible to be in a stable cornering position with the resultant of these two forces inside the contact patch. This means there must be other forces at work. Which?
Yes, you can lean your bike and travel in a straight line, but try it with the steering locked dead ahead and it will turn towards the direction of lean. Not a very sharp turn, but a turn nonetheless. The contribution of bike lean angle to turn radius is given in one of the equations on that Wikipedia link in my earlier post.



Fajita Dave said:


> This makes it sound like you're talking about camber thrust but your original challenge was about leaning your body while keeping the bike upright. So camber thrust wouldn't be a factor.


You're so close! That's almost the answer. I should clarify if I was ambiguous previously: the bike isn't upright (at least not when I do it), it's leaning into the corner a bit, it's just that the body is leaning more.

There's a big clue in the composite pic of Bobbi Watt performing three different cornering styles on this LeeLikesBikes page*. Apart from the body position and the lean angle of the bike, what's different between the three pics?

*With thanks to Harold of this parish, who I stole the link from.


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## alexbn921 (Mar 31, 2009)

If you you lock your steering you will crash. Lol I'm beginning to think you don't have a clue what you are talking about.


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## Fajita Dave (Mar 22, 2012)

Grassington said:


> There's a big clue in the composite pic of Bobbi Watt performing three different cornering styles on this LeeLikesBikes page*. Apart from the body position and the lean angle of the bike, what's different between the three pics?
> 
> *With thanks to Harold of this parish, who I stole the link from.


The "bike more than body" photo was taken while counter-steering to initiate the turn. Otherwise its showing the effective lean angle of the body/bike system. Which is more or less her COG as we've been saying this whole time. Since none of this is relevant to BB height I think I'm done with highjacking the thread.

You could certainly know something I don't but I don't want to go so far off topic for this thread.


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## Smithhammer (Jul 18, 2015)

Those low bottom brackets, though...


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## Cleared2land (Aug 31, 2012)

Oh yeah...


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## cookieMonster (Feb 23, 2004)

tealy said:


> pedal strike = user error


:drumroll: /thread.


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## DIRTJUNKIE (Oct 18, 2000)

Oh My Sack! said:


> They absolutely do. Shortly after my experience I posted above, I bought a Race Face Turbine crankset in 170mm, down from the 175 Sram carbon I had. It worked famously at virtually eliminating pedal strikes on my toothy trail. I was SOLD! About a month into this experiment, I had a revelation and that was that I thought I was losing fitness for some reason. I couldn't figure it out, I was riding all the time but realized I had been struggling on getting up all the chunky tech climbs that I rode multiple times per week. I figured I was just going through some old guy phase so I didn't dwell on it. I was just about to hand over my Sram carbon crankset to a friend that wanted to buy it when I had the bright idea to throw it back on the bike just to see what it felt like in comparison to the 170's I had been riding for more than a month. NIGHT & DAY difference! That 5mm of leverage was amazing! I was back to my old self on the tech climbs. I'm so glad I tried the old cranks. They stayed on the bike and I sold the near new Turbines on pb.


I'm still on old geometry but after reading this ^ it seems there is no fix to pedal strikes and still have climbing leverage with 170mm cranks on new geometry. So I guess you just deal with it and change your riding style to avoid pedal strikes with new geo.


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## richwolf (Dec 8, 2004)

DIRTJUNKIE said:


> I'm still on old geometry but after reading this ^ it seems there is no fix to pedal strikes and still have climbing power on new geometry. So I guess you just deal with it and change your riding style to avoid pedal strikes with new geo.


Or wait till the new buzzwords are slack, long and high!

Someone will take it up eventually.


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## mikesee (Aug 25, 2003)

tealy said:


> pedal strike = user error


If ti happens once in a blue moon, sure.

If it happens repeatedly, on every ride, it's poor design.


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## richwolf (Dec 8, 2004)

Pedal strikes = Designer error!


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## Fajita Dave (Mar 22, 2012)

Tantrum cycles seems to have solved the low BB pedal strike problem . I wonder what a high BB short chain stay bike would handle like.


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## alexbn921 (Mar 31, 2009)

I think that we can all agree:
Low BB handle better.
Pedal strikes suck.
Flip chips to adjust bb height have no downsides.

BB height is very terrain specific. Designers are riding a fine line tiring to get as low as possible while maintaining clearance.

BB height is not a static measurement. Tire size, sag, fork length, crank length, pedal width all affect our perception of too low. I find it easy to change my BB with all the adjustments available.

Some of this is technique to avoid pedal strikes and some is not having super rocky trails. I added 10mm to my fork, run super thin pedals, have a 2.5 tire on the front, 175mm cranks and run the chip in low.


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## Grassington (Jun 24, 2017)

Fajita Dave said:


> The "bike more than body" photo was taken while counter-steering to initiate the turn. Otherwise its showing the effective lean angle of the body/bike system. Which is more or less her COG as we've been saying this whole time. Since none of this is relevant to BB height I think I'm done with highjacking the thread.
> 
> You could certainly know something I don't but I don't want to go so far off topic for this thread.


We can assume Bobbi has initiated her turn already and is into the meat of the corner, but yes, that is the correct answer and a shiny rep point is in the post to you. Some nice powers of deduction and impressive knowledge of bike dynamics there, Fajita Dave.

A pic might be useful so I'll be cheeky and download it to mtbr (not hotlinked, I'm not _that_ rude). Atone for my sin by visiting the excellent LeeLikesBikes.









Notice the difference in steering angle between the 3 pics. With the body-leaned-more-than-the-bike the only way this can be stable is to introduce another force to keep the bike from falling over. In the absence of a strong sidewind, this is done by turning the steering harder into the turn, which produces a rotational force that compensates for the misplaced CoG (this is the same force that initiates a countersteer move). The downside is that the greater slip angle of the front wheel eats away speed. So... if you lean your bike harder (and assuming you don't run out of grip or clip a pedal), you'll maintain more speed through a corner because the reduced slip angle of the front wheel isn't scrubbing away so much speed.



alexbn921 said:


> If you you lock your steering you will crash. Lol I'm beginning to think you don't have a clue what you are talking about.


Yeah, that was my point - you can't go in a straight line with your bike leaned without compensating with the steering. It is true that the more I learn the more I appreciate how truly ignorant I am, and I'd never come across camber thrust until Fajita Dave mentioned it - I shall look into that, might be useful. It's worthwhile having a play with cornering lean angles as it really does make a difference to speed. That's within the limits of grip, of course, and also pedal clearance... and 3... 2... 1... - thread back on track 

Regarding bottom bracket height then: it's complicated, possibly more complicated than steering and I reckon we've just proved how complicated that is. It can't be taken in isolation because when a frame designer changes the bottom bracket height* the whole frame geometry has to change to accommodate this. It's pretty much accepted that low BBs are more stable but make the bike less nimble, and high BBs give faster handling but the bike is more work to control. I like my bikes twitchy and I don't like pedal strikes, so I do hope this low BB thing is a passing fad. When I clip a pedal on my 2004 Marin, it's my fault. When I clip a pedal on my 2017 Ghost, it's the bike's fault.

* The more reasonable spec is bottom bracket drop, which is the vertical distance between rear wheel axle and BB axle.


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## richwolf (Dec 8, 2004)

Grassington said:


> Regarding bottom bracket height then: it's complicated, possibly more complicated than steering and I reckon we've just proved how complicated that is. It can't be taken in isolation because when a frame designer changes the bottom bracket height* the whole frame geometry has to change to accommodate this. It's pretty much accepted that low BBs are more stable but make the bike less nimble, and high BBs give faster handling but the bike is more work to control. I like my bikes twitchy and I don't like pedal strikes, so I do hope this low BB thing is a passing fad. When I clip a pedal on my 2004 Marin, it's my fault. When I clip a pedal on my 2017 Ghost, it's the bike's fault.
> 
> * The more reasonable spec is bottom bracket drop, which is the vertical distance between rear wheel axle and BB axle.


But BB drop has less to do with BB height overall because it depends upon tire diameter and front fork Axel to crown measurement.
Why is my BB height lower on my Stache with a 2.6 tire vs. a 3.0 tire? It would be even lower with a 3.0 tire in a smaller diameter wheel.
Why do I notice no difference on my Stache with a lower BB with my smaller diameter 2.6 tire vs. a 3.0 tire? In fact I feel the 3.0 tire and resulting higher BB handles better plus I get fewer pedal strikes. I guess there is less "operator error" for me with a higher BB!


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## Varaxis (Mar 16, 2010)

Love the amount of physics discussion in this thread.

Angular momentum applies to this too, right? When a mtber pumps terrain, they are using angular momentum to speed themselves up. When they push their CoG away from the tire contact point when going up a ramp, they will speed up as a result of reducing the radius of the ramp, which is based on the combined CoG of rider and bike. This should also apply at least to berms, which is exemplified by pro DHers pushing into berms halfway through for greater exit speed. But what about for unbanked turns? Doesn't increased speed cause your turn to go wide, as it's limited by traction? I'm thinking that such unbanked turns simply have speed limits, based on traction and the amount of space you have to maneuver, and that BB height doesn't make a significant difference. I'm guessing it's more of a feel preference, with low BB being more forgiving to those entering turns a bit too hot. That or they have to go in harder to make up for the speed loss from having a lower CoG, if angular momentum also applies.

BB drop, on the other hand, improves stability, which can increase confidence and traction by keeping the wheels in more consistent contact with the ground.

BB height's effect on cornering might be one of those easily misperceived feelings, like how smaller wheels _feel_ faster than bigger ones, due to the perception of increased feedback being normally correlated to high intensity and speed. Could be a hypothesis worth experimenting with. I have a ROS9 with an EBB, and trails worthy to test on less than 5 mins from my door. Hmm...


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## Sideknob (Jul 14, 2005)

tealy said:


> pedal strike = user error


Depends - if my 4x4 or dirt bike bottoms out regularly on average terrain or comes to a dead stop from hitting a small, average sized obstacle, is it fit for purpose?

Comes back to what I said earlier about modern 4x4's design being market driven - designed more and more to suit soccer moms and getting lower to the ground and less suited to offroad use.

MTB design features have also always been market driven - and not necessarily to suit everyone let alone more "core enthusiasts" I guess you'd call them.

An "all mountain" bike for example is only so much use if it's too low to regularly clear inconsequential obstacles and geared too high for extended climbs or steep and techy climbs. And yet there is a preponderance of AM bikes with low BB's and non-low gearing. Again, possibly market driven by folks who want to coast downhill and so forth as opposed to the few who want to grind their guts out going up and over to enjoy the downs.

I've had more pedal strikes in the 12 months I've had a 150mm AM bike than I've had in 23 years of owning rigid bikes then hardtails and then a 100mm XC dually (which did it moreso than the rigids and HT's too....) I've killed two pedals stone cold dead on objects I never even noticed while JRA.

If I was damaging my 4x4 while JDA (Just Driving Along) while not even expecting a bottom-out, would that also be user error?

I don't think so.


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## richwolf (Dec 8, 2004)

I think the OP has different setups with effectively lower BB's
He has a Stache with 29 by 2.6 tires and 27.5 by 3 inch tires. I imagine he ran it with the stock 29 by 3.0 tires.
Did he even say what bike he hit the pedal with that left him on the deck and what the BB height is?
I like the idea of testing bikes with different BB settings be it through tire size or something like an EBB and seeing if the handling differences are worth increased pedal strikes.
Since I have ridden hardtails with 29er, 27.5 plus and 29 Plus from 2.6 to 3.0 I would say the lower BB tradeoff is definitely not worth it. Do people try to go with the smallest diameter tire on their bike to lower BB?? No, usually they go to bigger tires because tires have a much greater impact on how the bike goes down the trail than BB height. Low BB height is over rated.
I can't really speak as to Full suspension but there is no way you can have a ton of travel and not have to compensate with a higher BB or just put up with pedal strikes all the time


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## Charlie Don't Surf (Mar 31, 2017)

richwolf said:


> I think the OP has different setups with effectively lower BB's
> He has a Stache with 29 by 2.6 tires and 27.5 by 3 inch tires. I imagine he ran it with the stock 29 by 3.0 tires.
> Did he even say what bike he hit the pedal with that left him on the deck and what the BB height is?


At the time with a 120mm fork at 25% sag the BBH was 270mm or 10 5/8" with my favorite 27.5, 2.8 Nobby Nics. I didn't mention it earlier.... but I never thought this thread would get this much activity either.


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## singletrackmack (Oct 18, 2012)

Charlie Don't Surf said:


> At the time with a 120mm fork at 25% sag the BBH was 270mm or 10 5/8" with my favorite 27.5, 2.8 Nobby Nics. I didn't mention it earlier.... but I never thought this thread would get this much activity either.


What bike did you have the 27.5" 2.8 nobby nics on?

10 5/8" is a extremely low BB height.


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## *OneSpeed* (Oct 18, 2013)

alexbn921 said:


> I think that we can all agree:
> Low BB handle better.





Grassington said:


> It's pretty much accepted that low BBs are more stable but make the bike less nimble, and high BBs give faster handling but the bike is more work to control. *I like my bikes twitchy* and I don't like pedal strikes, so I do hope this low BB thing is a passing fad.





richwolf said:


> In fact I feel the 3.0 tire and resulting higher BB handles better plus I get fewer pedal strikes.


Clearly a variety of preferences, and yes it's more complicated than singling out one number on a geometry chart. I think it's largely dependent on location, the bike in question, and riding style. There's no one size fits all.

I'm forever curious about geometry. I also prefer a nimble bike though that's probably largely because of where I learned to ride and my local terrain. That said, I loved my Krampus on these same trails. That bike didn't get around tight switchbacks very quick, and it had a long wheelbase, and worst of all it had long chainstays, but it was still a blast.

I think for certain bikes (fat bikes in particular) it requires a reset of your mentality and expectations. IMO some people get too caught up on "my fat bike doesn't handle like my XC race bike" or sometimes people are too weight conscious about all the wrong things. *I like all my bikes because they are all different, not in spite of it.* They each do different things well.


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## Fajita Dave (Mar 22, 2012)

*OneSpeed* said:


> I think for certain bikes (fat bikes in particular) it requires a reset of your mentality and expectations. IMO some people get too caught up on "my fat bike doesn't handle like my XC race bike" or sometimes people are too weight conscious about all the wrong things. *I like all my bikes because they are all different, not in spite of it.* They each do different things well.


I think cyclists are very "sensitive" to even slight changes. Especially road cyclists. Disc brakes added 3/4lbs to my bike and costs 1 watt of aero efficiency at 30mph!!!! The F$^*@ing world is ending!!!

I haven't ridden to many bikes in my 7 years of mountain biking. I do find it pretty easy to adapt to the strengths and weaknesses of different bikes though. It just takes a little time and be mindful of it. Everything with bike design is give and take. My bike's BB height is dead on 13" but I've demo'd a few that were much lower. I LOVED how one of those bikes rode. Short chain stays, low BB, long front end... I would sacrifice a lot of other characteristics to have that playful "let it all hang out" handling. Bombing downhill stupid easy to pop a manual and tons of confidence to hit any trail side jump or drop.


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## Charlie Don't Surf (Mar 31, 2017)

singletrackmack said:


> What bike did you have the 27.5" 2.8 nobby nics on?
> 
> 10 5/8" is a extremely low BB height.


That's my Airborne Griffin, it's over 11.6 now with 140mm fork, and DT Swiss XM521 35mm rims


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## singletrackmack (Oct 18, 2012)

Charlie Don't Surf said:


> That's my Airborne Griffin, it's over 11.6 now with 140mm fork, and DT Swiss XM521 35mm rims


It looks like it the griffin comes stock with a 3.25" front tire and a 3" rear. What is the stock BB height?

Going from a 3.25" down to a 2.8" wide tire is going to lower the intended Bb height by at least half an inch. And if those 2.8" wide tires actually measure more like 2.6" wide like many of them do, then the BB will end up even lower.

I don't know for sure, but I don't think the griffin was designed to run tires as small as those 2.8" front and back.


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## richwolf (Dec 8, 2004)

singletrackmack said:


> It looks like it the griffin comes stock with a 3.25" front tire and a 3" rear. What is the stock BB height?
> 
> Going from a 3.25" down to a 2.8" wide tire is going to lower the intended Bb height by at least half an inch. And if those 2.8" wide tires actually measure more like 2.6" wide like many of them do, then the BB will end up even lower.
> 
> I don't know for sure, but I don't think the griffin was designed to run tires as small as those 2.8" front and back.


My wife has a Griffin and with Specialized 3.0 tires on it the BB height is around 11 7/8 inches which is low. I am sure this is probably just a 29er frame converted to 27.5 plus. I wouldn't go with a smaller tire on this bike.

This whole low BB trend might have more to do with trying to use existing stock to reconfigure bikes and then trying to use lower BB's as a selling feature.

I laugh at this whole "new geometry" hype. This is brought to you by the industry that:

Gave us biopace
**** ass shifting systems
Super narrow bars
Super wide bars
Understay roller brakes
Super narrow rims for MTB
1.95 tires
Alloy nipples
Questionable cable routing
Hard to service Bottom Brackets
Trek Y bikes
All sorts of stupid suspension designs
One by systems that leave people wanting for more range and can be super expensive.

What really makes you think they are always getting it right now?

Now don't get me wrong there are lots of great advances but if you have to shorten cranks, get thin pedals, ratchet and readjust your whole riding technique then something smells fishy to me! Just so you can rail the turns!


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## Charlie Don't Surf (Mar 31, 2017)

singletrackmack said:


> It looks like it the griffin comes stock with a 3.25" front tire and a 3" rear. What is the stock BB height?
> 
> Going from a 3.25" down to a 2.8" wide tire is going to lower the intended Bb height by at least half an inch. And if those 2.8" wide tires actually measure more like 2.6" wide like many of them do, then the BB will end up even lower.
> 
> I don't know for sure, but I don't think the griffin was designed to run tires as small as those 2.8" front and back.


Stock was 50mm wide rims too, the 2.8 with the 35 ID rims only lose about 1/4" total OD, but your on point either way. Designed for? Pfffft! Half the reason I MTB is to try stuff! All that aside, I'm back to "stock" bb height after the 140mm fork and updated rims.... plus the bike is way more playful to boot


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## singletrackmack (Oct 18, 2012)

richwolf said:


> My wife has a Griffin and with Specialized 3.0 tires on it the BB height is around 11 7/8 inches which is low. I am sure this is probably just a 29er frame converted to 27.5 plus. I wouldn't go with a smaller tire on this bike.
> 
> This whole low BB trend might have more to do with trying to use existing stock to reconfigure bikes and then trying to use lower BB's as a selling feature...


That could be. It used to be much simpler with just 2 wheel sizes, now add the plus thing in the mix and companies using the same frames sold with different wheel sizes without changing the geo. That's alot of variation in BB height.



Charlie Don't Surf said:


> Stock was 50mm wide rims too, the 2.8 with the 35 ID rims only lose about 1/4" total OD, but your on point either way. Designed for? Pfffft! Half the reason I MTB is to try stuff! All that aside, I'm back to "stock" bb height after the 140mm fork and updated rims.... plus the bike is way more playful to boot


Of course trying different set ups is allways fun. No doubt. But bikes used to come stock with smaller tires (2.1, 2.2 maybe 2.3) and often not very good, so the first thing to be changed was to put a new, and most likely bigger tires on the bike. Going smaller than stock meant maybe .1 to .2 of a difference and most probably didn't do that anyway and got bigger and grippier tires instead.

I have two old school rigids that run 11.6 inches in BB height with stock 1.95" tires. One bike has 1.95 tires on it and I have to be very careful to avoid pedal strikes in rough terrain. The other bike has some big 2.4" tires and there is a noticable difference in BB/pedal clearance with those tires. An 11.5" bb height with a sus fork seems exessively low to me and I could see why your having issues.

However, if the griffin is actually a 29er frame and your running 27.5 2.8" tires then I wouldnt chaulk up pedal strikes due to low BB trends, but rather extreme equipment choices. I dont think going smaller than stock tires is a good idea in general and especially if your getting into bikes sold with plus tires.

Increaseing frok travel is smart if set on small tires though, but if you want playful, why not a 27.5/26" hardtail with some beefy 2.4" or 2.5" with reasonably wide rims like i25 or something?


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## Charlie Don't Surf (Mar 31, 2017)

The Griffin was based off s Goblin EVO 120mm 29 2.4" tire setup, they changed some geo and added big vol + tires in 2015. The 2.8 are better, period. The Vee tires were ok, but they were really limited on a serious trail, plus I wanted to try the most aggressive 2.8 I could. We have the Griffin 27.5 + 2.8, An Orbea Loki 27.5 + 2.8 and a Stache 29 3.0 thru 2.6


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## jim c (Dec 5, 2014)

Fajita Dave said:


> I do find it pretty easy to adapt to the strengths and weaknesses of different bikes though. It just takes a little time and be mindful of it./QUOTE]
> 
> This is exactly how I see it, the few bikes I've been super familiar with rode quite differently, but I enjoy each one for their strengths. I'd love to try my current bike (Process 134) w/ longer 175 cranks just to see if that 5mm change makes it easier to climb. If that's true it'd surprise me.


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## High_Plains_Drifter (May 29, 2011)

I have two bikes that are easily adjustable between steep/slack. A Knolly Delirium (354/345) and a Knolly Warden (345/337). I've tested both settings on a variety of different trails. 

Cornering at high speeds is noticeably better in the low setting. I can tell a big difference at speed. It's surprising considering that it is only about a cm difference. The head angle does also rake out, so I need to keep my body position a bit more forward to prevent wash-outs up front. Other than cornering, I can't list any other benefits than I can tell. On technical climbing trails, I have way more pedal strikes. I ride flats and these are long travel bikes, so that doesn't help.

Having a bike that can be switched is nice. For Moab, Sedona and our tech trails in NM, I always run in the steep setting. For flow trails like 18 RD and Dupont SF, I loved having the Warden in Slack..


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