# tall rider. is a longer or shorter crankarm length better?



## bykesick (Dec 27, 2016)

I'm 6.4 and wonder what crankarm length is better or if it doesn't matter too much. Maybe just advantages and tradeoffs for each one?.

it would be on a single speed setup and so I wonder if this is possibly even more important.

I was told that shorter arms would help me up the hills, but I heard from another person that I would want to get them in the longest length I could without it hitting the ground or any sort of obstacles.

Are longer crankarms the same as a bigger ring and shorter arms are the same as a smaller ring?.

at my height would I actually have an advantage with longer arms?.

I think my height already gives me a lot of natural leverage.

I have 170mm cranks now, but oddly wonder if 175s might also increase the comfort of my saddle.

The reason I mention that is because of how my other bike is a lot more comfortable for long periods and it uses 175mm cranks which might mean a lower straighter leg position.

does crankarm length also affect seat comfort?.

the real question though is what I mentioned originally with regard to advantages and my torque and what is truly the best for a tall rider?.


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## RAKC Ind (Jan 27, 2017)

Can't really relate ring size to crank arm length. Reason is that rear cog plays an equal part in how everything plays out.

A 5mm difference isn't going to make a difference in saddle comfort. That's a fit/saddle problem.

In a technical sense 5mm or 10mm longer cranks give you more leverage over a given chainring. This is why some say to use the longest cranks you can. But in a real world sense they are wrong.

However personal ergonomics come into this as well. The little difference you may find in crank arm length may or may not be as comfortable or efficient for you. 

Using the same chain ring size your legs travel a shorter distance on shorter crank arms vs longer arms per revolution.

There's a lot more that can go into it but things like range of motion etc all come into play.

Only way to know what works for you is a longer crankset.

A plus of shorter cranks all that aside is a tad more ground clearance at the pedals.

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## *OneSpeed* (Oct 18, 2013)

some people recommend determining crank length by inseam length, not overall height. you should probably be on 180's. 170 is too short. On a SS, i think a longer crank has more advantages than drawbacks, for a taller rider even more so. 

saddle height is how you adjust leg extension, not crank length. if your leg is too bent when the pedal is in the down position, raise your saddle. 

there's plenty of threads on the subject if you search. there's also online crank length calculators if you google.


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## khardrunner14 (Aug 16, 2010)

I have 170's on one bike and 175's on another... never notice a diffrence or think about it at all. My inseam is pretty dang long like 36"ish.


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## Cotharyus (Jun 21, 2012)

News flash. Crank arm length has little or nothing to do with height. Also, your leg shouldn't be straighter at the bottom of a stroke with a 180 crank than with, say, a 160. You seat should be adjusted based on leg extension at the bottom of your pedal stroke, and leg extension should be the same regardless of crank length. Shorter crank? Raise your seat up the amount that the crank is shorter. Now, of course a lot of taller people like a longer crank, that's no contest. But I know a guy going on 6'6" that rides 160s because it keeps his legs straighter all the time and reduces stress on his bad knee.

That brings us to gearing, power, and how shorter cranks affect riding the bike from a standpoint of riding as opposed to fit. The amount of power you make will be the same. It's sort of like adding another gear ratio in your drive line though to consider crank length. What happens is, with a shorter arm, you can spin the same gear faster, although you lose some leverage when you get to a hill. So you might be faster on flat sections of trail, but you might have to work a little harder to get up hills. But who are we kidding, this is the single speed forum right? If it was easy, we'd be somewhere else.


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## Sparticus (Dec 28, 1999)

RAKC Ind said:


> ...
> In a technical sense 5mm or 10mm longer cranks give you more leverage over a given chainring. This is why some say to use the longest cranks you can. But in a real world sense they are wrong.
> ...


Obviously you have a reason for saying this. Do you mind if I ask what it is? Thanks.
--sParty


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## captainblacksox (Oct 25, 2011)

I am faster uphill with 180mm cranks than 175. Not sure why but it is consistent each time I switch.


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## WillTheGreat (Aug 26, 2010)

captainblacksox said:


> I am faster uphill with 180mm cranks than 175. Not sure why but it is consistent each time I switch.


That's because you have more mechanical advantage. It is the same effect as going down about 1 chainring tooth. You can generate more torque at low speeds at the cost of top speed.


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## SeaBass_ (Apr 7, 2006)

I'm 6'3 with a 34 inseam. I used 180's on my SIR9 and liked them but when I went to a different frame that had a lower BB, I would get too many pedal strikes so I went back to 175's.


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## Ryder1 (Oct 12, 2006)

If you want to geek out, check this link out. Dude gets into venous return, lactate thresholds, muscle fiber type, etc., but I think the most important factor is cadence: longer cranks for slower cadence, shorter cranks for spinning. SSing for most is about slow-cadence climbing, and will prefer a longer crank (I sure do), or at least want to avoid a shorter crank (like being 6'4" and SSing with a 170mm).

Eat Sleep Train Smart - Personal Training & Coaching Official Blog: Crank Arm Length: Everything You Need To Know


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## asphaltdude (Sep 17, 2008)

> It's the only component on the bike that directly affects the only two ways you can produce power- the amount of torque you can generate and the rate that it can happen.


Nah.

Crank length influences gain ratio just as chainring size, sprocket size and wheel size do


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## Ryder1 (Oct 12, 2006)

without a named source, that's "fake" news...

Ring/sprocket/wheel size are transmitting the power output, not affecting torque or power input.


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## asphaltdude (Sep 17, 2008)

Ryder1 said:


> without a named source, that's "fake" news...
> 
> Ring/sprocket/wheel size are transmitting the power output, not affecting torque or power input.




















Classical mechanics is neither news, nor an opinion. 

Longer crank decreases gain ratio = 'easier'
Larger front chainring increases gain ratio = 'harder'
Larger rear sprocket decreases gain ratio = 'easier'
Larger wheel diameter increases gain ratio = 'harder'

So yes, of course an SS bike with 32/18 and 180mm cranks will climb 'easier' than the same bike with 32/18 and 170mm cranks, as the 180mm cranks actually provide a lower gain ratio = lower effective gear.

Riding the same bike downhill you won't spin out as fast on 170's, as they actually provide a higher gain ratio than 180's.


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## RAKC Ind (Jan 27, 2017)

Ryder1 said:


> without a named source, that's "fake" news...
> 
> Ring/sprocket/wheel size are transmitting the power output, not affecting torque or power input.


Think someone slept through math and science classes in grade school 

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## Ryder1 (Oct 12, 2006)

Yeah, I understand all that. We all do. I think the quoted sentence was referring to the rider/crank relationship, not the bike's transmission of power, hence the phrase "two ways you can produce power [torqueXrpm]" but I did find, when I read the article, that sentence to be awkward. Hardly matters. Nitpick all you'd like.



RAKC Ind said:


> Think someone slept through math and science classes in grade school


My SAT math score was 99th percentile. What was yours, smart ass?


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## mountainbiker24 (Feb 5, 2007)

I forgot where I read this, but I spent an afternoon researching crank arm length a little while ago. There is more to the leverage thing than just assuming longer cranks have more leverage. It also has a lot to do with how your knees align with the pedal stroke and the angles in which your knees generate the most power. Long story short, many people may benefit from running much shorter cranks than they currently are. I'm 6' 3" with long legs/femurs, and I really like the 172.5 cranks on my road bike, and I would like to run shorter cranks on my mountain bikes.


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## RAKC Ind (Jan 27, 2017)

First, was giving you crap because you didn't read the OPs entire post and take all questions into account for your response, asphalt and I did. He asked about exactly what was answered.

Won't start comparing all that "standardized testing" scores.

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## Ryder1 (Oct 12, 2006)

RAKC Ind said:


> First, was giving you crap because you didn't read the OPs entire post [...]


I read it. He asked many questions. Just chiming in. But thanks - been here for 10 years and yours is my first insult IIRC.


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## RAKC Ind (Jan 27, 2017)

Wasn't an insult man, WAS A JOKE lol. Being a bit thin skinned today?

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## Sparticus (Dec 28, 1999)

asphaltdude said:


> ...
> 
> Classical mechanics is neither news, nor an opinion.
> 
> ...


So it really comes down to personal preference. There's no advantage or disadvantage to long cranks or short ones when gearing is adjusted to make the work equal. Is this a fair statement? (I really don't know, but it sounds like it is based on your diagram and narrative.)

If it is a fair statement, then it seems to me that rider preference is all that matters. My long legs prefer 185-195mm cranks and I adjust my gearing from there. Somebody else may prefer 165-170mm cranks and they can set up their gears to provide the range they like best.

This is one of the aspects of cycling that I like best. Every rider gets to build a human powered machine that (s)he feels serves him/her best. What others think really doesn't matter, it's that person's machine and to each his/her own. Cool. Are we lucky people or what?

--sParty


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## Cotharyus (Jun 21, 2012)

Sparticus said:


> then it seems to me that rider preference is all that matters.
> --sParty


Nailed it.


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## wayer (Feb 17, 2014)

This discussion seems to be conflating two separate topics.

1) Ratio between one rotation of the pedals and one rotation of the wheel.

This is impacted by crank length, front & rear sprocket size, and rear wheel size.
If you change one variable (crank length), you can adjust the overall ratio between the pedals and rear wheel by changing the sizes of the front and rear sprocket.

2) The bio-mechanical efficiency of a pedal stroke for a particular size rider.

Changing your crank length will change the ratio between the pedals and the wheels, but that isn't the reason to change your crank length (except on a single speed). Usually the reason to experiment with crank length is to be able to get more power into your pedals and improve rider comfort.

With a metabolic cart, an ergometer a vari-crank installed you could test your metabolic efficiency for a given crank length at a fixed wattage. You'd get a chart that would show you your optimal crank length - assuming that your goal is maximize your ability to turn O2 into watts!

Here is an example chart of https://www.alancouzens.com/blog/CrankVO2.jpg


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## TwiceHorn (Jun 18, 2014)

wayer said:


> This discussion seems to be conflating two separate topics.
> 
> 1) Ratio between one rotation of the pedals and one rotation of the wheel.
> 
> ...


In theory they are separate and conflated. A longer crank will provide more torque for a given force applied at the end of the crank, optimally tangent to the circle that the end of the crank circumscribes, or at a right angle to the crank at any given point in that circle.

But the problem is that a human rider doesn't apply a force that neatly. Not even the most technically proficient rider does for any significant portion of the 360 degrees of rotation. And the variables there are so many that the mind boggles at attempting to quantify them.

So you're right, you can only really determine the effect empirically and blanket statements about crank length are pretty much useless.

I suppose that you can generalize that the reactive force applied by the longer crank to a rider's foot is larger, in that tangent direction most of the time, but even that starts to lose significance once things start turning. And that, again, doesn't tell you much about whether it's good or bad for a given rider.


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