# why are wheels and 'spinning weight' important?



## yellowwducky (Jan 1, 2004)

Hi all,

I read on a site that wheels are the first place to look to reduce weight. This site mentioned that the rotational weight of wheels make a big difference on acceleration, turns etc. Any thoughts why this is? I am trying to get as light a bike as reasonably possible for my wife so if this is the best place to do achieve that I would love to know what kind of wheels to get for her to help.

Regards,

YD


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## Trevor! (Dec 23, 2003)

Hey,

Here is my simple view of it:

Spinning the cranks drives the rear wheel which in turn gets the front wheel moving too. When you pedal a bike you have to use energy in getting the wheels to turn. 

You use more energy to move a heavier wheelset (Tyres, Tubes, Rim tape, Rim, nipples, spokes, hubs) per revolution then you would with a lighter wheelset.

I would rather have to exert energy upon a wheelset that weighed 1600g then on one that weighed 2600g.

Very very simple, non scientific answer. Hope that helps.

Trevor!


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## yellowwducky (Jan 1, 2004)

i guess i was thinking wheels were pretty close in weight. i am going to make a bold statement that i am pretty sure lighter wheels cost more money! ah, this is going to hurt trying to lighten up my wife's bike. maybe the extra weight would help her get in better shape should be my selling point?!


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## Trevor! (Dec 23, 2003)

yellowwducky said:


> i guess i was thinking wheels were pretty close in weight. i am going to make a bold statement that i am pretty sure lighter wheels cost more money! ah, this is going to hurt trying to lighten up my wife's bike. maybe the extra weight would help her get in better shape should be my selling point?!


Your average 1650g wheelset like am classic hubs mavic rims supercomp spokes are very realistically priced!

Wheelsets around the 1350g wheelset are over priced and not worth it IMHO for MTB unless your racing elite and need every little saving...

Cheapest way to save weight:
Tubes
Tyres
Rims
Spokes
Rim Tape
Grips
Saddle (Off ebay)
Handle bars (Off ebay) You can get carbon Hyperlight flat bars for $40 from jenson!

Trevor!


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## yellowwducky (Jan 1, 2004)

so looks like you gotta go tubeless tire as well then. oh the budget is getting creamed! now that i look at it though, you are right, lot of weight to be saved on wheels - the diff between 2600g and 1600g is 2.2 pounds! that is almost 10% of the total weight. thanks for the advice Trevor!!

yd


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## Boj (Jan 13, 2004)

It is a fact that rotational weight on wheels influences acceleration of the bike but in case of MTB this is greatly exaggarated within this community. Commonly quoted is that gram saved on wheels is worth 2 grams. Here are the actual numbers where a gram saved is worth this much on a particular part (and only for cases of acceleration):

hub 1.0007
spokes 1.2043
rim 1.7006
tube 1.8723
tire 1.8723

wheel overall

front 1.563
rear 1.467

Most important thing to note is that this is only the case for acceleration which is not an important performance parameter in MTB as rarely you are accelerating and most of the time going at constant speed grinding up a hill or on a flat. My point is that saving rotational as opposed to static weight has only very small theoretical and no actual real world advantages. In line with that I'd advise you to save weight where it gives you the best gram saved/$$ ratio regardless of weather its rotational or static mass.


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## yellowwducky (Jan 1, 2004)

Thanks for that BOJ.

Looks like there is some physics at work relating to distance from the axis of rotation. Cool. Regardless, I am going to try and shave as much off as reasonably possible from my wife's bike so that she can have a good experience and will continue to want to ride.

yd


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## Guest (Jan 21, 2004)

*acceleration*

to the person who claims you are rarely accelerating in mtb then he should be able
to ride a single speed, he doesnt need gears. when you slow down or speed up at all
that is an acceleration!


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## bianchi4me (Jan 13, 2004)

*"constant speed" ?!?*

You must do your "Mountain Biking" in a stadium. Out on the trail your speed is *constantly* changing, not remaining constant. I'm in FLORIDA, one of the flatest places on earth, and I'll see speeds of anywhere from 5 to 22 mph when riding mixed single-track/fireroad/pavement routes. For people with serious elevation changes, it's even worse. You never slow down for corners? Your trails are always perfectly flat? You never sprint to pass someone? What planet is this that you're talking about?

It sounds like your analysis would be more suited to someone setting the World Hour Record in a Velodrome, and some, but not all, Triathalon events. Even normal road Crits involve huge amounts of acceleration and braking on a tight course.

There's a reason why top pro riders dis their sponsors and spend $3000+ of their own cash on custom-built ADA wheels, but put up with "off-the-shelf" sponsored hardware on the rest of their bike.


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## bianchi4me (Jan 13, 2004)

*Wheels rotate at twice the ground speed of the bike.*

The mass at the outer edge of a wheel travels at twice the speed of the bike over the ground. The reason for this is that it is traveling through two directions. The bike is only moving forward in a (theoretically) straight path. The mass of the wheel is rotating, so it's moving not only forward but also must travel an equal amount up-n-down as it travels through a circular path.

So to accelerate the mass of your frame to 20 mph, you have to accelerate the wheel to 40mph at the outer edge. Obviously, it takes more energy to accelerate the mass of your tire or rim to nearly 40mph than it does to accelerate the same amount of mass in or on the frame to only 20 mph.

Tires are the best place to look for weight savings for this reason.


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## Boj (Jan 13, 2004)

I was simply stating that case for rotational weight is WAY overrated in case of MTB.

I am aware of acceleration in MTB being present (and what acceleration is to the other poster) at tight twisty singletrack or any place that offers sudden possibility of pedalling hard, however in vast vast majority of races I've raced and places I've ridden it is a matter of grinding up a hill or flats with no MEANINGFUL accelerating taking place. What I mean by meaningful is acceleration that would justify distinction between rotational and static weight. Human motor does not supply enough power to give huge accelerations and hence the effect of rotational mass is really not significant to be worshiped as it is.

The fact that you ride in Florida where it is all flat makes for a more twisty/tight singletrack makes for more pronounced acceleration when riding. However even in Florida if you have 500g lighter wheelset than your buddy and he has a 500g lighter frame than you I assure you the difference in acceleration (about 250g worth) between you two thanks to the rotational effect is not worth consideration. Across the distance of a 1.5 hour race, even in Florida, the roatational effect of your lighter wheels would be worth 1-3 seconds advantage maybe. Far more important parameters would be your power output, overall mass (bike + rider), rolling resistance of the tires etc.

On the other hand if you had a 500g lighter wheelset and your buddy had 750 g lighter frame, your bikes would accelerate the same however he would have actual weight advantage of 250 g (as opposed to percieved with rotational mass) which would be easily worth more than 1-3 seconds in a race in saved rolling resistance or any hill climbing.

My point is simply that acceleration is a negligable factor in MTB and hence rotational effect of wheels shouldn't be given such great publiity as it is given. When it comes to saving weight save it where ever your $$ best allow you to, wheels or frame alike.


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## fonseca (Jan 12, 2004)

*I'm not a weight weenie...*

...But based on my own experience I completely disagree. I notice a huge difference switching between two tires of the same model/tread/durometer, one kevlar, the other steel bead with heavier casing. That's a difference of 800g or so, and I feel it for the entire ride. Yet I don't discern any difference in how fast I'm going between a full water bottle and an empty one, or my 100oz Camelbak when half full or at maximum capacity.

I don't have lap times to back that up, but I'm sure someone has done similar experiments. I'm betting a bike with a two pound weight attached to the frame but light tires will be considerably faster than a bike with no weight on the frame and a pound of weight on each wheel, at least on typical singletrack. I'm not sure what the results would be were the times recorded on a perfectly flat paved road, but I bet that even the smoothest spinners in the world still have slight deceleration and acceleration with each pedal stroke.

Every pedal stroke is an acceleration, followed by a slight deceleration, over and over. I can easily notice a difference of just 100g when I swap tires, but I can't tell whether I'm running my DH or XC BB or not.

I don't think rotational weight is overrated at all.


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## yellowwducky (Jan 1, 2004)

I think i am going to just err on the side of shaving off as much as possible - esp for my wife. 2 pounds can be saved on wheels so that is a big start. another pound on shock maybe if i can find something that will work for her yet be lighter and still reliable. given her light weight, I am sure everything will support her; especially with her conservative riding style.

as per the discussion at hand, I can see both sides. it would seem to me that acceleration would definitely be impacted in a big way when you start up but I am not that convinced that once you are pedalling away on the flats that it would really matter - yes each stroke is an accel/decel but since you are only maintaining a speed rather than trying to build a speed up I would think the effect would be minimal then. so for a mostly flats rider the accel/decel thing not that important but for someone with say a straight into technical and then accel over and over again would matter. around here our trails are ups and downs which wouldnt be too tough to maintain speed over - except for fact that the bottoms are always technical so you always are at the slowest speed in the dip and have to get that damn bike up the other side so weight in general and the spinning effect i would think would be very important for my wife and i.

my 2 cents - i am not a physics major!


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## Trevor! (Dec 23, 2003)

fonseca said:


> ...But based on my own experience I completely disagree. I notice a huge difference switching between two tires of the same model/tread/durometer, one kevlar, the other steel bead with heavier casing. That's a difference of 800g or so, and I feel it for the entire ride. Yet I don't discern any difference in how fast I'm going between a full water bottle and an empty one, or my 100oz Camelbak when half full or at maximum capacity.[...]
> 
> Every pedal stroke is an acceleration, followed by a slight deceleration, over and over. I can easily notice a difference of just 100g when I swap tires, but I can't tell whether I'm running my DH or XC BB or not.
> 
> I don't think rotational weight is overrated at all.


Rotational weight is not overrated at all - I agree 100%

I totally understand what you mean by: 
*Yet I don't discern any difference in how fast I'm going between a full water bottle and an empty one, or my 100oz Camelbak when half full or at maximum capacity.*​
A water bottle adds around 770-800g of weight to your bike as the water weighs 750g if it is 750mL an the bottle is some more yet I would never really notice a big difference in how my bike rides. It still feels flickable etc.

I think one of the reasons why we don't notice the added or lost weight when we have consumed the water is because that weight is nearer the center of our gravity. Yet if it was further away from the bike we would.

So it seems rotational weight is not overrated at all.

Interesting about a water bottle because the only way I can feel a difference is if I lift the bike.

Trevor!


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## Low_Rider (Jan 15, 2004)

I definiately notice the difference between a pair of full and empty waterbottles - I guess I need to work on my muscle tone...........  

dave.


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## Boj (Jan 13, 2004)

While I would question anybody's ability to 'feel' 800g difference on tires or anywhere, rolling resistance is more significant reason why your tires may feel faster.

Rolling resistance is the greatest opposing force in MTB and when changing from one tire to another differing rolling resistance properties (which change from steel to kevlar belted tires) would be the most significant reson a tires would feel faster or not. Lets not forget that you are carrying 800 g less mass and whatever difference in body weight between the runs. To make comparison fairer you should fill your bottle full when switching to lighter tires (though that still leaves difference in rolling resistance of the tires to compensate for). Either way the rotational mass (ie acceleration) would play a part, but not a significant one. Other effects would overshadow it by far.

It would take a lot of dedication to set up a proper experiment. You would need to have same tires and different wheelset, but thats not enough. It would be impossible to compensate for riding technique as no 2 runs in the singletrack even of the same rider are the same. Having just a straight line race would probably be better though that wouldn't prove that there is little acceleration in actual MTB riding. Whats more important is that there is no need to measure it, as the effect of rotational mass is simply proportional to how much a bike accelerates. Show me how much acceleration there is in a MTB race and I'll tell you how much faster you go because of rotational mass. The truth is not much.

Every cyclist does indeed have power on and power off in the pedalling stroke. When the pedal stroke is on, you accelerate and when the stroke is off you decelarate. However while reducing mass helps accelerate faster when the stroke is on, it is actually slowing you down when the stroke is off because the bike loses momentum faster with less mass (ie decelarates faster just as it accelerates faster). That is why there is little dynamic effect at constant bike speed (effect of just slight acceleration/deceleration due to pedalling forces) for change in rotational mass. To judge the effect of how rotational mass changes you have to have the whole bike system accelerating like from 0-20 kph, 10--20 and such. The effect from just pedalling mostly cancels itself out.


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## fonseca (Jan 12, 2004)

Boj said:


> While I would question anybody's ability to 'feel' 800g difference on tires or anywhere, rolling resistance is more significant reason why your tires may feel faster.


I can feel just a 100g difference in tires. Heck, I can easily feel the difference between my DH tubes and my Specialized thin tubes. When I rebuilt my spare wheelset last week I was reaching into a bag of brass and al nipples and selecting the brass ones by weight in my palm. You don't have to believe me. I'm not a gram counter at all, my Titus Switchblade is pushing 30lbs, and that's my primary XC bike.

Most of my riding has lots of short, steep hills, where I am out of the saddle hammering all the way up. That's acceleration/deceleration at it's most apparent. Light tires and rims make a big difference in how easy it is to get to the top.

I don't think rolling resistance is the reason I notice such a difference, as I mentioned above I have two sets of tires with identical tread and durometer. How does a steel bead and thicker sidewalls affect rolling resistance when I'm running them both at the same pressure?

The plus of DH tires and tubes is the gyroscopic effect can carry me over rock gardens and obstacles in a way that light setups don't. Is it all my imagination? I wouldn't be swapping tires all the time if I didn't feel a substantial difference.


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## Boj (Jan 13, 2004)

I'm sorry, no disrespect to you (there are numerous people here who say stuff like that) but you can't feel 100 g difference. If the question was would you be able to feel 100g difference in a blind test I'm sure you'd fail to prove this ability. When you know the bike is 100g lighter its human nature to feel it faster but in a blind setting where you don't know what bike is lighter you can't really tell the difference. If you don't believe me consider this:

Your body weight in a course of a day can vary by up to 2 kg depending on how much you eat/drink and how much you leave behind you. Around 1 kg total change up and down is about standard variation that I was able to find pretty much every day when I poped on the scales (and I only weigh about 65 kg). Across long term this is even more as your body accumulates and loses fat.

So your body weight fluctuates by up to 1000g every day, which easily dwarfs 100g change on the bike. My point is that your body weight is far greater source of mass fluctuation and nobody ever picks a difference in ride there every time they throw a leg over saddle. If you are contending that decisive difference is that weight is rotational, it is still apparent that 1000g would have far geater effect on your acceleration than about 200g worth of apparent rotational weight.

Its not my intention to completely discount feel as a means of assessing performance but it has to be used in conjunction and under thorough critical examination of speedo, stopwatch etc. Often this is not possible (eg stiffness) and even if this is done, it doesn't guarantee accuracy - what power you put for example varies readily but is rarely measured in any experiments on bikes. It is SO difficult to achieve similarity between different runs on a bike yet so many people on this forum regularly claim performance difference using simply their assomometers without considering anything else.  

Lighter tires/rims will always climb faster than heavier ones and heavier tires/rims will always be more stable than lighter ones. That's not in contention. I'm simply argueing that inertia effect of the saved rotational mass (the infamous each gram saved is worth 2) does not translate into any actual gains as compared to simply saving equivalent static weight.


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## heatstroke (Jul 1, 2003)

*here is some maths for you*

simplified : 
You're going to do some work going from zero to 30kph
Assume that you + bike weigh 80kg & each wheel weigh 2kg

Linear kinetic energy = 1/2mv^2 = 0.5 *80kg* (8.333m/s)^2
= 2777.8 joules

rotational energy = 1/2(moment of inertia) * angular speed^2
= 1/2(m*r^2) * 22.62 radians/s
= 69 joules (per wheel)
= 138 for 2 wheels
So rotational energy contributes about 5%

What happens if you stick on tyres which weigh 150 grams more your total weight goes up by 0.375% but : 
linear kinetic goes up to 2788 (0.375%)
rotational kinetic goes up to 149.3 (8%)
total energy increases by 0.74%

i.e you do disproportinately more work....

i've simplified the moment of inertia assuming all the mass is on the rim.


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## Boj (Jan 13, 2004)

*And here's some more...*

a = M/[r*(2*m1+2*m2+m3)]

where:

a - acceleration (m/s^2)
M - torque at the back wheel (N*m)
r - radius of the back wheel (m)
m1 - mass of the front wheel (kg)
m2 - mass of the back wheel (kg)
m3 - static mass (rider + rest of the bike, kg)

Also can be expressed as

a =[1/(2*m1+2*m2+m3)]*(M/r)

For Bike 1, 80 kg bike + rider and 2 kg each wheel thats:

a1 = 0.01190476*(M/r)

For bike 2, the same 80 kg bike plus rider (ie frame heavier 300g) but 150g lighter each wheel:

a2 = 0.01194743*(M/r)

Which means that if we use the same input power (torque, M) and same wheel radius (r):

a1/a2 = 0.996428 (meaning that bike 2 accelerates about 0.36% faster, YAY).

Now how much faster is that in a 0-30 kph sprint:

t1/t2 = a2/a1 = 0.996428^-1 = 1.003585

Now 0 - 30 kph takes about, say, 4 seconds in a good sprint on bike 1 (insert any number you find reasonable here):

So thats t2 = 4/1.003585 = 3.9857 seconds

t2 - t1 = 4 - 3.9857 = 0.0143 seconds

So in conclusion, by having 150 g lighter each wheel and 300 g heavier frame you go faster in a 0 - 30 kph sprint by a grand total of (...carry the y, square root, plus grand total equals...) whopping 0.0143 seconds. At 30 kph that means bike B will be ahead by all of 11.9 cms


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## heatstroke (Jul 1, 2003)

*4seconds to 30 means about 700 watts*

could also calc time by assuming a given rider power. You know the how much linear and rotational kinetic energy needs to build up at 30kph. So if you know the power output, you can calc the time.

at 700 watts, time difference to 30kph = 0.014 sec
at 300 watts, increases to 0.034 sec


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## Trevor! (Dec 23, 2003)

Boj said:


> a = M/[r*(2*m1+2*m2+m3)]
> 
> where:
> 
> ...


Brilliant post - I think that sums things up quite nicely indeed! Puts weight into perspective for us!

OT: Do you do math's or physics for a living?? I am impressed by all of the above....

Trevor!


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## B R H (Jan 13, 2004)

*Engineering baloney.*

Basic physics cannot be so easily applied to such a complex problem. One blatant erroneous assumption is that of constant input power. The human engine is no such thing. The "extra" mass added by the inertia of heavier wheels takes it's toll fairly quickly on the relatively tiny power output of the human motor.

The same simplistic math could be used to prove that a rider can't be faster climbing hills with a full suspension bike due to the heat lost in the damper due to bobbing (most other things being equal).

There are just so many variables in these types of calculations that it's not even funny.

Don't forget that these same "engineers" are the ones that design all sorts of products that fail every single day in the real world while everything on paper says a failure was impossible! Take a stopwatch with you on rides and try doing some testing of your own to see how it compares to those simple theories. You just may be surprised by what you discover.


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## heatstroke (Jul 1, 2003)

*engineering sausage*

assuming 1 kg and 5" diameter, that sausage would take less than 1second to hit 30kph assuming a constant 300 watts.


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## fonseca (Jan 12, 2004)

And no disrespect to you either, but as I already said, I absolutely *can* feel a 100g difference in tires when riding. I guess you skipped over the spoke nipple example above, but I can easily feel the .65g difference between a .35g al nipple and a 1g brass one. Anyone possessing basic cognitive ability and functioning hands can do the same. Try it yourself, put one in each hand and if you can't tell them apart every time, something is wrong.

I don't think your comments about body weight fluctuations are at all relevant to this topic, except perhaps that it reinforces my belief that wheel and tire weight is much more important when riding than weight on my body such as a hydration pack, or weight in the middle of the bike closer to my center of gravity. Even a 2kg fluctuation is only ~2% for me, so no, I don't think I would notice that. But we're talking about an object which we are constantly expending energy to propel and turn, not body weight.

A 100g+ weight difference between a 500g and 600g tire, however, on a 900g wheel...that's a huge difference. Not to mention that the wheels are located out in front of me and behind me, so in addition to acceleration, every time I lift up my front end over a log with my arms, and then the back wheel with my legs, my bike is acting like a beam with a spinning weight on the end.

I'll tell you another anecdote. On my other FS bike I briefly ran an oem Manitou Black Sport before I got a great deal on a Black Super Air. I bought it only for the tunability that air gives, but I was amazed at how much easier it suddenly was to lift my front wheel over roots and logs. Only later did I learn that the Super Air was more than half a pound lighter. Let me guess, that's rolling resistance too? 

I believe your formulas are far too simnplistic and don't account for many variables. Foremost the fact that we do not put out constant power when riding, and our speed as a result is fluctuating with every pedal stroke before you even factor in the constant acceleration and deceleration necessary on switchbacks, rock gardens, short climbs, etc. I'm not a physicist, and neither do I play on on mtbr. But I contend that saved rotational mass does in fact translate into actual gains, such as less expended energy on my part.

Finally, I do maybe 1-2 races a year. I'm not interested in shaving a few seconds off lap times, which weight reduction from anywhere on my bike would absolutely do. What I am interested in is a bike with the lightest tires I can get away with that still have great traction when I'm riding XC. If I had a choice of moving two pounds from my tires to my frame or vice versa, you know which I would choose. It may be subjective, but I believe most riders can easily notice the difference lighter tires and rims make.

I think we can agree to disagree. If I'm a poor misguided biker living in a world of my own misconceptions, then here I am content to remain. I'll stand by the saying that an ounce on the wheel is worth a pound on the frame.


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## Titus Maximus (Jan 3, 2004)

heatstroke said:


> assuming 1 kg and 5" diameter, that sausage would take less than 1second to hit 30kph assuming a constant 300 watts.


My, what a big sausage! And such incredible thrust!


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## Axe (Jan 12, 2004)

Boj said:


> I'm sorry, no disrespect to you (there are numerous people here who say stuff like that) but you can't feel 100 g difference. If the question was would you be able to feel 100g difference in a blind test I'm sure you'd fail to prove this ability.


I had a chance to had such blind test. My friend usually rides light tubes. I spinned around a parking lot on his bike and mentioned that it felt a bit sluggish. Well, he switched 99 gram tubes for 170 gram ones.

VERY noticable. I was not looking for that.

You still can be sure as much as you like, though..


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## Low_Rider (Jan 15, 2004)

You've all forgotten one thing.... the mental aspect!!  

Yeah, so realistically you might not truly experience any real performance difference by loosing 100grams, but mentally, that can be a huge boost to your perceived performance. The lighter tires I put on my rims to race on probably don't make any real difference physically, but boy oh boy, I'm sure I feel faster, and probably push myself harder because of it!!  

Cheers, Dave.


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## Chester (Jan 15, 2004)

fonseca said:


> Finally, I do maybe 1-2 races a year. I'm not interested in shaving a few seconds off lap times, which weight reduction from anywhere on my bike would absolutely do. What I am interested in is a bike with the lightest tires I can get away with that still have great traction when I'm riding XC. If I had a choice of moving two pounds from my tires to my frame or vice versa, you know which I would choose. It may be subjective, but I believe most riders can easily notice the difference lighter tires and rims make.
> 
> .


I agree with you that the lighter tire will increase your performance. However I suspect that perhaps you do not fully understand rolling resistance. I used to think that the tread and tire pressure were the main subjects which affected rolling resistance. I couldn't have been more mistaken.

You said...

..".But based on my own experience I completely disagree. I notice a huge difference switching between two tires of the same model/tread/durometer, one kevlar, the other steel bead with heavier casing. That's a difference of 800g or so, and I feel it for the entire ride"

What I discovered is that a small difference in rolling resistance produces far greater improvements in performance than significant reductions in weight. From what I can see in your posts, you may misunderstand. You seem to be saying that between two almost identical tires you get a 800g difference per set. First of all, I've never seen such a huge difference in two tires (same model/tread/durometer). That would be 400 grams per tire.
Normally I might see about 100 grams per tire or about 200g per set. 
Never the less, I would still suggest that most of the increase in performance you would feel would be from the probable reduction in rolling resistance between the two tires (same model/tread/durometer). There WILL be a difference in the rolling resistance of the two tires. Tread pattern, etc is not the defining matter when evaluating rolling resistance. 
Take two tires....same model, tread etc..same psi...the only difference being one has wire bead and one has kevlar etc. And the wire bead one may be worn to the point of being almost smooth, while the kevlar (lighter one) is full tread..... Some people would think the smooth wire bead one will certainly have less rolling resistance since it has worn almost smooth.....but the truth is that even with the more resistant tread the lighter kevlar tire will probably have a lower rolling resistance.....
The difference between the two almost identical tires you were comparing was almost certainly mostly due to the lower rollling resistance rather than the loss of weight, even as great as you said it was....at a amazing 800 grams. I have spent a lot of time looking into rolling resistance compared to weight savings both on wheels and on the bike in general and have come to a firm conclustion....

"There is almost.....no amount of weight loss on a bike....that will add as much perfomance to a rider as will switching to the lowest rolling resistance tires that will suit your needs. Suit your needs means.....if you are doing some very intensive downhilling etc.....much larger tread and beefier tires may be more important to you than rolling resistance. But if you can find two tires which give you sufficient grip, then you should always opt for the ones with the lower rolling resistance....even if they are heavier....
As I said, it takes a lot of weight to offset the performance gained from lower rolling resistance. You would be amazed... I would much rather have a 5 pound heavier bike with very low rolling resistance tires ....than the lighter bike with average rolling resistance tires... As I said in the beginning, I used to think otherwise, but I have become a convert....because it is true.

You also said the following....

"I can feel just a 100g difference in tires. Heck, I can easily feel the difference between my DH tubes and my Specialized thin tubes."

Here is a some data from some tests on tubes and rolling resistance...

first of all some rolling resistance measures of different tubes.measured with the same tire and the same pression: 
Continental Latex: 140g - 16.3 watts 
Schwalbe Standard: 180g - 18.1 watts 
Schwalbe Extraleicht: 96g - 18.3 watts 
Schwalbe Leicht: 127g - 19.1 watts

Now those are standard and light tubes... If one was to include something like your DH tubes you could find a much greater difference in rolling resistance per tier. It could be as much a 5 watts per tire...for a 10 watts total for the set of heavy DH vs Specialized thin.
10 watts is HUGE......HUGE.......
Most of the time you are riding, you are only putting out perhaps 250 watts.....
Think about it, those two tubes can suck up or give back 4% of your power without you even knowing it. You have attributed it to weight....but think about it....If you weigh 160 and your bike is 25 pounds, then your total weight in kilos is 84 kilos...
That 100 grams amounts to only 1 part per 840 in weight difference... Even if you double it because it is way out on the tire......it is still only about 1 part per 420.
Compare that ratio to possibly using up as much as 4% of your power from poor rolling resistance......
And think about it.......that is only on the tubes....
It is not hard at all to pick up 10 watts on a set of tires compared to another set.

It steals power away from you and most riders attribute it all to weight.....

Math isn't everything but when differences are so huge, you have to pay attention to what the facts are telling you....
People who harp on about rolling resistance do so because they have usually looked into it in some detail.. Most others focus on weight almost exclusively...


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## yellowwducky (Jan 1, 2004)

wow, this has been a great post - and unlike in some forums fortunately this has not resulted in a shtt slinging match when people have disagreed.

seems to me the theories and conclusions are sound. i would bet that if i 'believed' differently though, that i would 'feel' differently when riding. it reminds me of golf clubs - my father insists no one can hit a one iron except god. i on the other hand believe it is a great club and can seem to hit it well where he always shanks it. now if i believed that a 1kg water bottle would be better than 100g on a wheel, maybe i would feel that my riding was faster with a water bottle penalty rather than a wheel weight penalty.

people have said the maths are not perfect because of not perfect inputs or what have you being applied to a complex problem. that said, if we cant use the formulas to explain the theoretical differences in a 'simpler' closed system, how can we then assume that because our 'assomometers' felt a ride was faster with a lighter wheel was indeed faster - the variables you pile on then make the complex problem even more complex from ride to ride - temperature that day, your weight change etc etc etc.

is 'assomometer' in the dictionary by the way?!


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## Boj (Jan 13, 2004)

Heatstroke

You are right at 700W thats 4 seconds and at 300W the 0-30 kph dash takes 9.26 seconds and the difference is 0.034 seconds. That is still very little. If for example one of the riders in question pumped up the watts to 500 for a couple of seconds they'd leave the other by 1.33 seconds. Just illustrates the insignificance of the difference that weight is rotational.

Also 700W is what I would expect any 70 kg rider to do in a sprint. A good sport/expert rider can get 300W average across a 1.5 hour race. Also good work on the sausage  


Trevor

Thank you. I am final year Aerospace Engineering student this year and hope to make a living of this, though most of my graduate friends this year are struggling to find jobs in the field. I hear Al Quaida pays well though 



BHR

I have had numerous heated discussions with some very intelligent people on this board, but from reading few lines of your reply, you are not one of them. 0-30 kph sprint is surely one of the simplest problems in physics and in case I am making unwarranted assumptions or missing variables you are quite welcome to point them out. Either way I hope that you don't consider your last reply an intelligent, well founded criticism any more than I do.

There is no implication that power is constant. I have constructed equations so that it doesn't matter what power you use. You simply enter the time it would take to do this sprint. 4 seconds (300W), 9 seconds (700W), you can put in any power, it doesn't matter really. If your issue is that power output varies across such a sprint, you are welcome to construct the most optimistic power v time graph you can fathom and I'll be happy to input it into equations and still show you how little difference between two test riders there is.

As for the rest of your crap I won't bother replying (because anyone reading this for the physics knows its just that) except for one thing. It is those same engineers that design car that you drive, TV you watch, computer you are typing on and yes, even that bicycle you ride. Next time you want to look around you at anything in your world you are welcome to express gratitude to the same profession you are slagging.  


Fonseca

I didn't think nipples example was the same however Aluminium nipples are 3 times lighter than brass and I'm sure even I'd be able to tell the difference. What you are saying is that you can pick fraction of a percent change in performance just by riding a bicycle. The comments about body weight are relevant because that is a must larger object that you have to push when you pedal along. If 2 kg is only 2% weight difference 100g amounts to 0.001 % difference.

I'm not arguing that lighter wheel and fork won't be easier to lift or accelerate. I too want to shave weight off my bike anywhere I can and I spend lots of $$ on bits just as you do I'm sure. And saved rotational mass DOES indeed translate into less energy expenditure for you. Hell, if I had a choice I'd probably move 2 lbs off my wheels onto my frame. But I only recognize that the move won't mean any significant performance improvement. In a DH race, for sure, it would make more difference as you can win/lose DH race by 12 cm but I don't think its something noticable like you say it is. Anyway, no hard feeling - I agree to disagree 


Axe

I have a test for you. We get 50 pairs of bikes ranging from DH rigs to XC hardtails. Each pair of bikes is decked out identical except for 50g more on each wheel indistinguishable to the eye. You go out for a spin on each of them and identify which one is heavier. If you get more than 45 identifications right - I owe you a coke


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## B R H (Jan 13, 2004)

*You are still in school.*

That explains alot. Come back to this thread in 10 years and see if you are still as certain about things. One thing you may realize with time is that most problems that are easily solved have already been done so and the facts have been established and applied long ago.

This is one such case even though the mathematical proof may not be so easily shown. bianchi4me pretty much summed it up by pointing out where the pros stand on this issue. There is a lot of wisdom in experience. You will have to discover that on your own as I had to myself.

PS. Not that it matters, but I too can play engineer and, in fact, I do so on a regular basis as a consultant. I also have one client that is a large aerospace company, so be careful where you send that resume'.


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## Tbonius (Jan 13, 2004)

*It's all about seconds !!!!!!!!!!!!!*

Seconds man - are you nuts!?? Seconds are everything in racing....sheeesh - you act like 1 or 2 second differences mean nothing - YOU OBVIOUSLY DON"T RACE AT A HIGH LEVEL. There was more than one race last season where the only thing that separated 10th place from 5th place were seconds...less than seconds...or 5th place from 1st for that matter.......If you get a guy by half a wheel - how much time did you think passed dude?....according to you not enough to make a difference.... tell that to professional road sprinters....


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## divve (May 3, 2002)

There's a definite difference between road biking and off road however. With the constant jarring, slow rough sections, speeding up after a tight corners, I notice a clear difference in feel when I get in the area of 300g weight reduction. In road biking I don't notice anything at all unless I'm climbing a steep hill at a very low speed. Aerodynamics is still king over a large margin there.


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## tracker (Jan 22, 2004)

*Seconds Are Everything!*

I dont race alot but I time myself almost every ride. I literally kill myslef just to get extra seconds. So I 100% back the coment about seconds is everything.

And as far as tires are concerned. I use my supersonics on tracks that have alot of hills and twisty turns. On some courses where the high speed is more stable I will use a Rockster on because the speed is more steady and the rolling resistance is just as good without loosing pucnture protection.

Weight for me on the wheels is very very noticable. I notice a tire change, I dont notice a seat post change or a stem change.

If there is any place I would love to loose the weight it would be the rim. But also you have to watch cost, value and reliability. I own a set of 1475 gram hugi 204's / Mavic 517 rims.

I got mine on ebay for $203.00, brand new and included 2 tubes and 2 s-works roll X tires.
A steal Yes it was a steal but you will find no other set of tires and rims that is new and this light weight for this price. Just check out ebay every now and then and you will see a set. I have owned two sets of these rims. I buy them just because they are so cheap and then sell my other sets after one year.

Performance bike has some tubes that are like 74 grams for the 1.5-1.9 version


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## Disaster (Jan 15, 2004)

tracker said:


> I dont race alot but I time myself almost every ride. I literally kill myslef
> 
> If there is any place I would love to loose the weight it would be the rim. But also you have to watch cost, value and reliability. I own a set of 1475 gram hugi 204's / Mavic 517 rims.
> 
> ...


That is fairly light and seems like a good deal. I've never bought any set that went under 2000g for the wheelset. Maybe if I get into racing.

If you want to go really cheap, JensonUSA sells DeoreDisc/Rynolite rimsets for $90 bucks, 1120g frt, 1320g rr. Even cheaper? Jenson sells CR18/unknown disc hub wheelset for $70! 1,100g frt, 1270g rr. Cheap and lightweight? $90 for a DeoreDisc/DS-2 wheelset, 890g frt, 1,100 rr.

I have an old wheelset with Formula disc hubs and CR18 rims that has held up fine...though never been really beaten on.


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## pimpbot (Dec 31, 2003)

*I disagree*



Boj said:


> I was simply stating that case for rotational weight is WAY overrated in case of MTB.
> 
> I am aware of acceleration in MTB being present (and what acceleration is to the other poster) at tight twisty singletrack or any place that offers sudden possibility of pedalling hard, however in vast vast majority of races I've raced and places I've ridden it is a matter of grinding up a hill or flats with no MEANINGFUL accelerating taking place. What I mean by meaningful is acceleration that would justify distinction between rotational and static weight. Human motor does not supply enough power to give huge accelerations and hence the effect of rotational mass is really not significant to be worshiped as it is.
> 
> ...


 I installed some $5 superlight innertubes, and immediately felt a night and day difference... all over a 40g per wheel weight loss. The bike felt snappier, easier to change direction in tight stuff, etc.

The thing that is failing to get mentioned here is that the added mass to the outside edge of the wheel isn't getting accellerated at a 13" radius, it's getting accellerated at a 13" radius X the gear ratio. This makes a big difference in higher gears.

Take a broom with a removable handle and swing it around your head, now remove the broom's head and do the same. The head accounts for maybe 2/3's the weight of the broom, but with the head on the handle, it takes way more than 3/2 the effort to swing, prolly more like 3-6X the effort to swing around your head. Not doing the math in my head, at least.

I can't tell you how many buds of mine bought those cheap XT hub/Rhynolite rim sets, put them on their bikes and bi***ed and moaned about how piggy their bikes felt, when the only difference was 100g more at the rim.

I mean, I've strapped a 100g fender to my bike and didn't even feel the difference. Strap 50g to each wheel and I would.


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## Chester (Jan 15, 2004)

*Rockster rollling resistance?*



tracker said:


> I dont race alot but I time myself almost every ride. I literally kill myslef just to get extra seconds. So I 100% back the coment about seconds is everything.
> 
> And as far as tires are concerned. I use my supersonics on tracks that have alot of hills and twisty turns. On some courses where the high speed is more stable I will use a Rockster on because the speed is more steady and the rolling resistance is just as good without loosing pucnture protection.


Just curious, but what makes you think the rolling resistance of a Rockster is just as good as Supersonics?

One other note....be advised that the rolling resistance of the Roll-X tires is very poor in most of the versions, although I have not seen numbers on the S-Works version in particular.

I do agree with you that seconds are very important....at least to me and that guy I am beating up the long climb....


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## Chester (Jan 15, 2004)

*Snappier from weight loss or lower RR*



pimpbot said:


> I installed some $5 superlight innertubes, and immediately felt a night and day difference... all over a 40g per wheel weight loss. The bike felt snappier, easier to change direction in tight stuff, etc.
> 
> .


What makes you think the snappier performance was all from the 80 grams rather than mostly from lower rolling resistance?

Here are just a few differences in rolling resistance of tubes...Many other not listed could have far greater differences.

Here is a some data from some tests on tubes and rolling resistance...

first of all some rolling resistance measures of different tubes.measured with the same tire and the same pression: 
Continental Latex: 140g - 16.3 watts 
Schwalbe Standard: 180g - 18.1 watts 
Schwalbe Extraleicht: 96g - 18.3 watts 
Schwalbe Leicht: 127g - 19.1 watts

So you could easily get 2.5 to 3 watts or more difference from a single tube. Put them on both tires and it can, depending on which tubes were orginal and which tubes are switched to, lead to quite a difference in performance.

If indeed the previous tubes you used had poor rolling resistance and the new ones had low rolling resistance than the difference you noticed was probably more due to that than 80 grams less weight. As you can see from the numbers above.....lowest in a given brand of tubes seems to correlate to lower rolling resistance, although a lower weight tube in one brand may have worse performance than a higher weight in another brand..

I don't imagine we'll ever get a comprehensive rating of all tubes when we can't even get all tires.

Just out of curiosity, which brand and model of tubes did you switch from and to.....?
Any weight on the old ones and new ones?

As you may have seen in my previous post above, lower RR can make a huge difference in performance and it usually is many times greater than the gains from weight reduction.


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## Boj (Jan 13, 2004)

teambender said:


> If you haven't already.
> 
> http://www.analyticcycling.com/
> 
> ...


Hey thanks for bringing that up. I wasn't going to post here anymore but I went there and they have a section which calculates sprint performance for different wheelsets which uses the complete differential equations of motion, and for the case quoted above the actual difference btw bike 1 and 2 is only a fraction of what I predicted before (0.005 sec, 4.5 cm). If you didn't believe me earlier, you are welcome to play around there a little and see (if you need any help with numbers, ask me).

As for the claims of 'feel' it always reminds me of a friend of mine who claims his car does 0-100 kph in 7 seconds flat, and he knows this, of course, by counting the seconds in his head alongside watching the road at high speed and the speedo at the same time  Another debate over 'feel' where claims I always find interesting is the difference a condom makes but for the sake of PG rating of this post lets not go there. 

Difference in weight on wheels changes the handling of the bike and as such may give credibility to claims of feeling the difference. Through personal experience riding and my physics intuition I'm 90% sure claims of exceptional 'feel' there are BS just as well (after all they all are) - I just can't prove it here so I'll give you the benefit of the doubt. As for all the claims of 'feeling' a performance difference (ie detecting yourself going faster) from changing a pair of tubes, I can, and have, proven that BS through maths so you guys know where I stand on those, 100%


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## divve (May 3, 2002)

Do the climbing calculation. You'll find that weight begins to make quite a difference (300g-500g). A full lap of 5 miles off-road or whatever of slow rough terrain, some climbing and tight corners is comparable.


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## Chester (Jan 15, 2004)

*True but check out the "speed given power" tool*



divve said:


> Do the climbing calculation. You'll find that weight begins to make quite a difference (300g-500g). A full lap of 5 miles off-road or whatever of slow rough terrain, some climbing and tight corners is comparable.


I agree with you that the 300-500 grams will make a difference BUT if you think that is true, and it is, then you need to use some of the other tools on analyticcycling.com

Go to the "tool" section and bring up "static forces" and then click on "speed given power"

Then do some calculations changing the weight using 1 kilo as a change....going from say 100 kilos to 99 kilos (rider + bike) and see how much the speed changes.

Then do the same thing but change the watts of power 5 or 10 watts....and see what that does to the speed...

See the increase in speed you get from each and you will see how small the increase in performance (speed) is from dropping a kilo compared to the results from increasing power 5 or 10 watts... For our purposes we will assume that adding power is almost the same (not exactly) as saving power by using either tubes with lower rolling resistance or tires with lower rolling resistance or by using a notubes system..

Even tiny increases in watts almost always gives you more speed than even large drops in weight. It is amazing how much more bang you get out of lower rolling resistance, especially when you consider the low cost. 
Yet ask a hundred riders if they want a 2.2 pound (1 kilo) lighter bike or some faster tires and they will almost always go for dropping the 2.2 pounds even if it costs a bundle.

Check out the other thread on rolling resistance on the board now...

http://forums.mtbr.com/showthread.php?t=1807


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## divve (May 3, 2002)

No need to convince me  I'm not a "super" weight weenie myself. Both my road bikes and MTB are relative heavy by most standards here. They are however reliable and fast.


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## Motivated (Jan 13, 2004)

*Rationalization*



Boj said:


> It is a fact that rotational weight on wheels influences acceleration of the bike but in case of MTB this is greatly exaggarated within this community. Commonly quoted is that gram saved on wheels is worth 2 grams. Here are the actual numbers where a gram saved is worth this much on a particular part (and only for cases of acceleration):
> 
> hub 1.0007
> spokes 1.2043
> ...


Since I want to buy a new wheelset I suppose I need to rationalize the purchase by convincing myself it will make me more competetive at races. I'm mostly joking with that, but here it goes. 
First, constant speed up a hill IS acceleration. 
Second, there really isn't another area to save as much weight as with wheels. A standard set of wheels weighs 2.2 kg to 2.4kg, a $400 set of wheels weighs 1.7kg - a savings of over 500g. There isn't another component you can save that much. And a second set of wheels is just a good thing to have.
Third, according to analytic cycling and likely your own calculations, a lighter, lower rotational inertia wheelset will make a rider faster by several seconds over a long climb (or many repeated shorter climbs). I get a 5 second difference over a 5km climb comparing a 2.2kg wheelset to a 1.75kg wheelset.
Fourth, if a wheelset gets me to the top just 1 foot ahead of my competitor that probably means I will take the first corner at the top which puts me in control and is very important in a race.
Fifth, the human body is limited especially in that when putting out larger efforts the ability to put out low efforts for long periods is severely diminished. The point here is that for a rider to "pedal harder" to overcome a heavy wheelset they are significantly sacrificing their endurance. The classic example of this is 'how hard to I go from the start?' If I go out really hard in a race I know I'm going to suffer at the end. I think a heavy wheelset is the same thing - if it takes me 2 to 5 or even more watts to get them going it is going to really make me suffer over the long term.
Lastly, the recreational rider will not benefit much from light wheels and should probably spend the money elsewhere or just save it.

So, basically Boj, you are right, but only within the envelope you defined. Outside of that envelope you are wrong in this case. Sometimes an engineer has to realize that obviously lighter wheels are better, then go about trying to figure out why. Not the other way around. Also, your crack about Al Queda was not even funny.


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## ThaFurnace (Jan 12, 2004)

A= acceleration
V=velocity
t=time

A=dV/dt

=(V2-V1)/dt

When V2=V1,

A=0/dt=0. 

So if you are going up a hill at steady state (meaning that at each "snapshot" your velocity is the same) then there is no acceleration.


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## divve (May 3, 2002)

It is pretty funny when you consider Osama's dad is in deep with Carlyle and the president's dad works for them as well....


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## Disaster (Jan 15, 2004)

*$100 bucks for 2000g. $500 for 1,500g.*



Motivated said:


> Second, there really isn't another area to save as much weight as with wheels. A standard set of wheels weighs 2.2 kg to 2.4kg, a $400 set of wheels weighs 1.7kg - a savings of over 500g. There isn't another component you can save that much. And a second set of wheels is just a good thing to have.


I know of at least one wheelset that can be had for $100 that weighs 2000g. $500 seems about right for 1,500g. So it looks like about $400 for 500g. That is 80 cents a gram.

Depending on your bike there could be some other fairly inexpensive opportunities.

The OEM 6061 handlebar on my bike weighed 380g. I bought a 7020 200g bar for $28. That was 15 cents a gram.

The tires on my bike weighed about 750 grams. $40 dollars yielded a set of 550 gram tires. That was 10 cents a gram.

My chrome moly railed seat weighed 380g. The replacement 210g titanium railed seat cost $80. 47 cents a gram.

OEM stem 320g. $30 replacement, 200g. 25 cents a gram.

OEM LX cassette, 330g. $40 bucks for XT cassette, 260g. 57 cents a gram.

OEM Crankset, 850g. $60 LX L572 crankset, 650g. 30 cents a gram.

On my bike, at least, the wheels were down the list a bit in weight savings value.


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## B R H (Jan 13, 2004)

*Which is obviously not the case...*

unless your pedal stroke is perfect (impossible) and leg strength infinite (again impossible).


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## jjay (Jan 12, 2004)

*take a piece of string with a 1lb weight on the end of it*

and spin it around and around.

That 1lb gets a lot heavier...


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## divve (May 3, 2002)

jjay said:


> and spin it around and around.
> 
> That 1lb gets a lot heavier...


It's also a lot harder to stop once it gets going....aaaaahhh now everything is all muxed up again


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## Axe (Jan 12, 2004)

Motivated said:


> First, constant speed up a hill IS acceleration.


Mmm. No. Constant speed is constant speed.

Your work lifting weight up is dependent only on the overall mass of the bike/yourself. It does not depend on the internal energy: that what rotating wheels have.

You need to do work to accelerate wheels to a constant angular speed. You do not have to apply extra work to lift them up the hill.


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## Axe (Jan 12, 2004)

jjay said:


> and spin it around and around.
> 
> That 1lb gets a lot heavier...


It does not. Tension in the rope gets higher. This tension does no do any work - it is perpendicular to the weight path.

1 lb is 1 lb is 1lb.

But, why you say, I am getting tired when I do no work? Because your body gets tired mostly from stress, not from work. It is a physiological problem - not purely mechanical.


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## Motivated (Jan 13, 2004)

*Ooops*



Axe said:


> Mmm. No. Constant speed is constant speed.
> 
> Your work lifting weight up is dependent only on the overall mass of the bike/yourself. It does not depend on the internal energy: that what rotating wheels have.
> 
> You need to do work to accelerate wheels to a constant angular speed. You do not have to apply extra work to lift them up the hill.


Yeah, I screwed up. Embarassing. I was quickly thinking of F=ma and summation of forces, but there is still acceleration - gravity balancing with the rider. That is bogus on many fronts.

Anyway, the problem with using analyticcycling.com is that it assumes perfectly smooth rider power and straight velocity curve. So I thought of integrating the equations over a true velocity profile to more clearly highlight the benefit of a light wheelset. I could do that but it would take me a while and the velocity profile would be just a guess. So instead I summed the small time savings calculated using equations listed by Boj over a 1 hour ride. I looked at it two ways:

#1 total weight of rider and bike stays same - weight is taken from wheels and put on bike. Using 83kg rider, 12kg bike and comparing two 2kg wheels to two 1.75kg wheels I get a time savings of .003 seconds for every 1 second acceleration. For a 1 hour ride I figure 10% is spent accelerating, which means 360 seconds of acceleration for a total of 1.1 seconds of savings.

#2 weight taken from wheels is not put back on bike - this is like swapping a wheelset and riding. Same as above, but the total time saved is 2.2 seconds.

OK, these are woefully low numbers for a $400 expenditure. Maybe that is why Lance says it's not about the bike. Maybe I'm just totally missing something because the benefit of light wheels HAS to be more than 2.2 seconds. Help!


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## Chester (Jan 15, 2004)

*I think its a little higher*



Motivated said:


> Yeah, I screwed up. Embarassing. I was quickly thinking of F=ma and summation of forces, but there is still acceleration - gravity balancing with the rider. That is bogus on many fronts.
> 
> Anyway, the problem with using analyticcycling.com is that it assumes perfectly smooth rider power and straight velocity curve. So I thought of integrating the equations over a true velocity profile to more clearly highlight the benefit of a light wheelset. I could do that but it would take me a while and the velocity profile would be just a guess. So instead I summed the small time savings calculated using equations listed by Boj over a 1 hour ride. I looked at it two ways:
> 
> ...


I just plugged some of those numbers into the analyticcycling site and came up with a bit more time....even forgetting the rotational and acceleration aspects

Just dropping off the .5 kilo off the (bike+rider) over a hour ride I come up with something like the following..... flat course about 4 seconds over the hour, 1.5% grade about 10 seconds and 3% grade aboutr 18 or 19 seconds over the hour.
Now its hard to judge what a up and down cross country course is....equal to....with all its ups and downs.....but I don't imagine it averages much more than a 3% constant grade would......nor is it flat...
I used the "speed given power" tool for this "rough" calculation and just changed the weight to get the differences.

Not sure if that is the proper way to get even a "rough" look at the question.
Still, it sounds a bit closer to the truth than 1.1 or 2.2 seconds over a hour ride.


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## Trebor Strebor (Jan 18, 2004)

*Hey, Double J-izzy*



jjay said:


> and spin it around and around.
> 
> That 1lb gets a lot heavier...


What da hell you doin' in dis bb? Stickin' yo spoon in, foo? 

Leave da calcs to da Poindexters and just ride yo bike!  You piss em off and they will take their phasers off of stun!!


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## jjay (Jan 12, 2004)

*Sup Trebs?*

I been around here for a while... lurking mostly.
I like this crowd...they don't take themselves too seriously.  

JJ
you riding Carter tomorrah?


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## Boj (Jan 13, 2004)

Motivated said:


> Yeah, I screwed up. Embarassing. I was quickly thinking of F=ma and summation of forces, but there is still acceleration - gravity balancing with the rider. That is bogus on many fronts.
> 
> Anyway, the problem with using analyticcycling.com is that it assumes perfectly smooth rider power and straight velocity curve. So I thought of integrating the equations over a true velocity profile to more clearly highlight the benefit of a light wheelset. I could do that but it would take me a while and the velocity profile would be just a guess. So instead I summed the small time savings calculated using equations listed by Boj over a 1 hour ride. I looked at it two ways:
> 
> ...


Benefit of light wheels as compared to heavy ones is WAY more than 2.2 seconds but not due to rotational inertia phenomena and acceleration. They are simply lighter wheels = carry less mass = less rolling resistance, less weight to carry up a hill - parameters with far greater impact than acceleration. If you want to investigate these go to 'speed given power' at analyticcycling, certainly enough justification you'll find for a $400 expenditure so long you get them real light for the money.


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## Acme54321 (Oct 8, 2003)

Axe said:


> Mmm. No. Constant speed is constant speed.
> 
> Your work lifting weight up is dependent only on the overall mass of the bike/yourself. It does not depend on the internal energy: that what rotating wheels have.
> 
> You need to do work to accelerate wheels to a constant angular speed. You do not have to apply extra work to lift them up the hill.


Mmmm Maybe Not....

Going up hill is an acceleration, in the upward and forward directions, foward acceleration being negative of course.

Also, the comment about spinning a weight on a string, making the weight feel heavier does not apply to bicycles.

The only thing that wheel weight will affect is inital acceleration.


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## Trebor Strebor (Jan 18, 2004)

*No...*



jjay said:


> you riding Carter tomorrah?


No

I got a loaner rear wheel when I took mine in for service and went for a road ride today. Just before the rain started, as luck would have it. Maybe on Suday I'll go down there, if it's not too wet...

How many laps are you shooting for at the six hour?


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## jjay (Jan 12, 2004)

Trebor Strebor said:


> How many laps are you shooting for at the six hour?


 last year I did 6, so at least 7 this year.


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## Stevebiker (Feb 17, 2004)

*Try this in a bike stand*



Chester said:


> What makes you think the snappier performance was all from the 80 grams rather than mostly from lower rolling resistance?
> 
> Here are just a few differences in rolling resistance of tubes...Many other not listed could have far greater differences.
> 
> ...


 In the middle or big chain ring and maybe a middle cog or so, Spin the crank as fast as you can from a dead stop by hand. I was supprised at the effort it took. Then take the tire and or the tube off the wheel and do it again. It's a big differance and the effort is only put toward rotating the wheel.


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## Stevebiker (Feb 17, 2004)

*Try this with your bike on a bike stand*

In maybe the middle chainring and a middle cog or so, spin the crank as fast as you can from a complete stop. That will give you an idea on how much it takes to get just the wheels alone moving. Now remove the tire and-or the tube and do it again. There is a big differance to me. That's all I need to know.


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## Go Kart Motzart (Jan 2, 2004)

Stevebiker said:


> In maybe the middle chainring and a middle cog or so, spin the crank as fast as you can from a complete stop. That will give you an idea on how much it takes to get just the wheels alone moving. Now remove the tire and-or the tube and do it again. There is a big differance to me. That's all I need to know.


You're right, you will feel a huge difference. While your bike is in the stand the only force you are trying to overcome is the weight of the wheel and the weight furthest from the hub (the fulcrum in this case) becomes very important The problem is in the real world your wheel is attached to the ground and the resistance becomes the weight of the whole bike and rider making the tire and tube just a small percentage of the mass you are trying to accelerate.


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## Stevebiker (Feb 17, 2004)

*I agree that it is a small percent of the total mass but,*



Go Kart Motzart said:


> You're right, you will feel a huge difference. While your bike is in the stand the only force you are trying to overcome is the weight of the wheel and the weight furthest from the hub (the fulcrum in this case) becomes very important The problem is in the real world your wheel is attached to the ground and the resistance becomes the weight of the whole bike and rider making the tire and tube just a small percentage of the mass you are trying to accelerate.


 The whole idea was to isolate the energy it takes to turn the wheel from moving the whole bike so you can see how much differance weight on the rim of a wheel can make. The energy it takes to move say, 400grams is a fair amount more then you would think. I know it isn't very scientific but it is good enough to tell me that 400grams on the wheel is more important then on the rest of the bike. If you are gona try and save 400 grams on a bike ( a small percentage of the total weight) then that would be the first place I would look.


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## mward (Apr 7, 2004)

To add fuel to the fire... 

Last night I picked up a used bike from the bike shop because I wanted some of the parts off of it. 2 of the parts I wanted were the wheels. They're bontrager race rims and bontrager hubs. They're REALLY light. They've got those 345g kendas on em with ultralight tubes too. I slapped them on my training bike which normally has mediocre rims w/ wire bead smoothies on it. Holy freakin effin heart attacks. I felt like superman. Talk about acceleration. The bike felt completely different. Now.. I have a nice set of light rims on my epic and it feels fast and whippy like this, but not this fast.. (tires are 180g heavier though, each). I'm not sure if this is rolling resistance, or weight, or what, but I could hammer at a much higher speed than normal on my training course, 4-6 mph faster for extended periods. If you can get a set of really nice wheels, do whatever it takes. Upgrade that first. No amount of bling can make your bike feel like this.


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## B R H (Jan 13, 2004)

*Another thing to try...*

Take off your front wheel, hold the axle ends in your hands, and give it a spin. Now try to move the wheel side to side (like when standing and hammering). Then try simple turns. Now imagine how much the resistance you felt increases with speed (you'll be lucky to be able to spin the tire up to even 10 mph in your hands)! Also notice how quickly the wheel will slow when you are actually able to move it. When this happens on the bike (practically every pedal stroke or turn), it takes additional power to re-accelerate the wheel. These forces are not accounted for in any of the simple equations being spewed out to prove that rotating mass is no big deal. Just try this little experiment, along with the bike stand one mentioned above, and you'll see it is plainly obvious that rotating mass is very important.

PS. This is coming from an engineer with a good background in math & physics, so don't think I don't value these tools! Just beware that there aren't many engineers with enough experience to so easily solve these problems, but there are many arrogant enough to claim their equations prove the world is flat. It is flat by the way.


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## Boj (Jan 13, 2004)

Stevebiker said:


> The whole idea was to isolate the energy it takes to turn the wheel from moving the whole bike so you can see how much differance weight on the rim of a wheel can make. The energy it takes to move say, 400grams is a fair amount more then you would think. I know it isn't very scientific but it is good enough to tell me that 400grams on the wheel is more important then on the rest of the bike. If you are gona try and save 400 grams on a bike ( a small percentage of the total weight) then that would be the first place I would look.


When you isolate it to just the wheel of course you're going to feel this difference more pronounced. That still doesn't mean that that difference is significant when you're hammering on the trail with all your 180 lbs bike + rider mass.

In your stand experiment you are moving lets say ~1.5 kg of mass of rear wheel + tires. If you remove tires and tubes say it goes down to 1 kg. Thats a 33% reduction in mass of the moving system and rotational or not that's going to be easily noticed. Your experiment has been constructed to easily show the difference but its not applicable to real riding. To put this better in perspective your stand experiement is similar to you riding your bike with a 90 lbs trailer attached and then with no 90 lbs trailer attached.


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## Boj (Jan 13, 2004)

mward said:


> To add fuel to the fire...
> 
> Last night I picked up a used bike from the bike shop because I wanted some of the parts off of it. 2 of the parts I wanted were the wheels. They're bontrager race rims and bontrager hubs. They're REALLY light. They've got those 345g kendas on em with ultralight tubes too. I slapped them on my training bike which normally has mediocre rims w/ wire bead smoothies on it. Holy freakin effin heart attacks. I felt like superman. Talk about acceleration. The bike felt completely different. Now.. I have a nice set of light rims on my epic and it feels fast and whippy like this, but not this fast.. (tires are 180g heavier though, each). I'm not sure if this is rolling resistance, or weight, or what, but I could hammer at a much higher speed than normal on my training course, 4-6 mph faster for extended periods. If you can get a set of really nice wheels, do whatever it takes. Upgrade that first. No amount of bling can make your bike feel like this.


For the nth time reducuing mass on your wheels WILL result you to go faster and substantially too if you drop a lot of weight but not cause its 'rotational' mass. Absolute reduction in weight and change in rolling resistance are much more significant than any extra advantage thanks to 'rotational' mass.


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## Boj (Jan 13, 2004)

B R H said:


> Take off your front wheel, hold the axle ends in your hands, and give it a spin. Now try to move the wheel side to side (like when standing and hammering). Then try simple turns. Now imagine how much the resistance you felt increases with speed (you'll be lucky to be able to spin the tire up to even 10 mph in your hands)! Also notice how quickly the wheel will slow when you are actually able to move it. When this happens on the bike (practically every pedal stroke or turn), it takes additional power to re-accelerate the wheel. These forces are not accounted for in any of the simple equations being spewed out to prove that rotating mass is no big deal. Just try this little experiment, along with the bike stand one mentioned above, and you'll see it is plainly obvious that rotating mass is very important.
> 
> PS. This is coming from an engineer with a good background in math & physics, so don't think I don't value these tools! Just beware that there aren't many engineers with enough experience to so easily solve these problems, but there are many arrogant enough to claim their equations prove the world is flat. It is flat by the way.


Its the same effect as the bike stand experiment from above. You are isolating the effects of rotational weight in your hands and thereby you've successfully proven that rotational mass is important when you are spinning the wheel in your hands. On the trail you are moving a much more substantial mass than your wheels.

Also if you look to the other thread on this in my Matlab simulation I did go the extra step to account for accelerations due to pedalling inefficiencies and accelerations of the bike+rider system are recalculated every 1/48th of a second. The relevant results are posted there and that Matlab model is just as sophisticated in crucial areas as the one at analyticcycling.com. And while were on analyticcycling.com, if you don't believe what I'm saying, you can go there yourself to do some simulations and see if what I'm saying is true.


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## Chester (Jan 15, 2004)

*Rotational weight--or-- Why Johnny Can't Climb*



B R H said:


> Take off your front wheel, hold the axle ends in your hands, and give it a spin. Now try to move the wheel side to side (like when standing and hammering). Then try simple turns. Now imagine how much the resistance you felt increases with speed (you'll be lucky to be able to spin the tire up to even 10 mph in your hands)! Also notice how quickly the wheel will slow when you are actually able to move it. When this happens on the bike (practically every pedal stroke or turn), it takes additional power to re-accelerate the wheel. These forces are not accounted for in any of the simple equations being spewed out to prove that rotating mass is no big deal. Just try this little experiment, along with the bike stand one mentioned above, and you'll see it is plainly obvious that rotating mass is very important.


I'd feel much better about your "examples" if you had actually done the math to quantify them. As Boj said, they sound really impressive, but I'd like to see you put them into a formula where you are dealing with a 180 pound mass...bike + rider.

"Also notice how quickly the wheel will slow when you are actually able to move it. When this happens on the bike (practically every pedal stroke or turn), it takes additional power to re-accelerate the wheel. "

Tell me.....using your best estimate.........how much "re-acceleration" is needed on each pedal stroke. In other words, in the real world, how much did you decelerate in your slow-down episodes on every pedal stroke... 1/100 mph? or is it only 1/1000th mph of deceleration and the then needed re-acceleration?
Unless you can actually quantify it, then it might be no different than the effect of you trimming your toe nails before a ride......toenails being part of rotational mass given the actions of your feet..
You speak about the huge affect it would have when you are "standing and hammering" going from side to side. I'll assume you are talking about moving more than 12 mph when doing your hammering... If so then these micro measurments of the side to side movements eating up momentum, would pale in comparison to the greater forces of wind resistance. Tighter jerseys would be a much higher priority in thinking than rotational weight versus frame weight.

Where are all the discussions about aerodynamics if everyone is so worked up about the "vastly" greater impact of rotational weight versus frame weight?
So many folks seem to be obsessed with all their imagined acceleration.
Unless you can put some real numbers on all of this acceleration and deceleration, its all imaginery as to it actually creating a siginifcant greater value for rotational weight.

Numbers please, or some site that, using numbers, shows the HUGE impact of rotational weight versus frame weight for the typical rider.


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## mward (Apr 7, 2004)

Boj said:


> For the nth time reducuing mass on your wheels WILL result you to go faster and substantially too if you drop a lot of weight but not cause its 'rotational' mass. Absolute reduction in weight and change in rolling resistance are much more significant than any extra advantage thanks to 'rotational' mass.


I wasn't saying it didn't, professor. I was just saying wow, after reading all this discussion I got a new very lighter set of wheels and went faster. Yeah, I like it. You'll note, if you actually read the post, that I just said I didn't know why it was faster, it just is. Reason being, I'm not a physicist or engineer. Okay?


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## Boj (Jan 13, 2004)

mward said:


> I wasn't saying it didn't, professor. I was just saying wow, after reading all this discussion I got a new very lighter set of wheels and went faster. Yeah, I like it. You'll note, if you actually read the post, that I just said I didn't know why it was faster, it just is. Reason being, I'm not a physicist or engineer. Okay?


Sorry, I didn't mean to come off harsh. Friends? 

It truly makes no difference to our riding what we believe or not so lets not fight over stupid things like this. Group hug everyone!!! Come on...


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## Chester (Jan 15, 2004)

*No "group hugs", or the "rotationalists" win......*



Boj said:


> Sorry, I didn't mean to come off harsh. Friends?
> 
> It truly makes no difference to our riding what we believe or not so lets not fight over stupid things like this. Group hug everyone!!! Come on...


We must fight on.....stamp out ignorance.....and expose the bike industry's cruel marketing trickery.... Here, on this site, we still have over 80% of riders convinced by their "common sense" that rotational weight is 2 or 3 or even (I've read it) 7 times more impactful on performance than frame weight. Its just a heap of baloney without any scientific----mathematical---proof.
They swing buckets of water around their heads and say "See, your arms get tired"
They grab detached wheels by their pinkies and say....."see it takes force to move it from side to side" They do almost everything except put it into some well based formula and see what the truth actually is.
There are so many things in this world that at one time were thought to be "common sense" but were proven to be completely wrong when put to valid controlled testing.

Many if not most of the "common sense" ideas about rotational weight expressed here have about as much credibility as one sees for "cures" on all the alterntive health web sites...
Some ideas have been debunked for decades and yet you will still see people suggesting they are true.
I challenge any of them to show that over any normal cross country loop that rotational weight is equal in affect to more than 1.1 times frame weight
That challenge is only 1.1 to 1..........forget about 2 to 1 ....or 7 to 1........, Just show me that over a cross country course with up hill and down hill and level......that after you add up all the values that it is even 1.1 to 1
The ONLY way you might exceed this 1.1 to 1 ratio is if you were to ride this 12 mile loop doing full accelerations for 15 seconds, hitting the brakes, screeching to 1 mph then repeating that crazy process over and over for the entire 12 miles. In effect, doing a crazy style of riding that no one does. Otherwise the amount of acceleration is much much smaller in effect than most of these poster are assuming. They act like are seldom riding at a steady rate of speed for even 25 feet.........OH yes....I forgot about all those millions of "pedal-cycle" accelerations and decelerations. Yes, what are they? Was that a .01 mph pedal stroke acceleration on average during the 12 mile loop?

Put some numbers on it guys......or you are just doing what all of the pre-Columbus guys were doing when saying he would fall off the edge of the Earth...

There.....that should stir it up again...


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## mward (Apr 7, 2004)

They're coming to conclusions a priori. A Priori : Derived by or designating the process of reasoning without reference to particular facts or experience.

It worked great for Aristotle!


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## XC Jedi (Feb 8, 2004)

*As an Orthodox Rotationalist*



Chester said:


> We must fight on.....stamp out ignorance.....and expose the bike industry's cruel marketing trickery.... Here, on this site, we still have over 80% of riders convinced by their "common sense" that rotational weight is 2 or 3 or even (I've read it) 7 times more impactful on performance than frame weight. Its just a heap of baloney without any scientific----mathematical---proof.
> They swing buckets of water around their heads and say "See, your arms get tired"
> They grab detached wheels by their pinkies and say....."see it takes force to move it from side to side" They do almost everything except put it into some well based formula and see what the truth actually is.
> There are so many things in this world that at one time were thought to be "common sense" but were proven to be completely wrong when put to valid controlled testing.
> ...


I challenge you to prove that it doesn't. I have yet to see any numbers from you. I'll show you some numbers:

Okay, everybody raise your hands who thinks that rotational weight is more important than static weight. lets see, one, two, three.....hmmm, looks like you lose.

This is fun.....


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## Chester (Jan 15, 2004)

*Rotationalists and their danger to the future of cycling*



XC Jedi said:


> I challenge you to prove that it doesn't. I have yet to see any numbers from you. I'll show you some numbers:
> 
> Okay, everybody raise your hands who thinks that rotational weight is more important than static weight. lets see, one, two, three.....hmmm, looks like you lose.


There you go again, you extreme orthodoxed rotationalists, trying to confuse the issue.
We, myself and other rational participants, make a point, and you rotationalists try to characterize our side as completely unreasonable in an effort to confuse the reader.

eg..... "Okay, everybody raise your hands who thinks that rotational weight is more important than static weight"

You have once again ( a typical rotationalist tactic) suggested that anyone who disagrees with the exteme rotationalist dogma, is in effect saying that rotational weight is absolutely no different than frame weight. That is UNTRUE. We do indeed believe that rotational weight is different and is even of greater value.....HOWEVER we violently disagree about the relative impact of the different kinds of weight. We want proof of its so-called greater impact. Show us it is above 1.1 to 1 on a typical cross country loop.
Boj has already posted significant data to show the impact is under 1.1 to 1 on a typical ride......
But do rotationalist come back with any data of their own? NO.....

Instead rotationalists, when they're not posting misinformation,....can be frequently found outside of a typical LBS leafletting and chanting about the dangers of rotational weight..
"2 times, 3 times, even 7....rotational weight is anti Heaven"
They dance around glassey-eyed while the owners (parts-pushers) inside the door stand there with approving smiles..... In walk the true believers...paying outrageous prices for titanium spoke nipples.....while ignoring much heavier frame weights....

I tell you sir, its a kind of sickness, this "rotationalism", and its ability to cloud the logic of otherwise intellegent people. 
But we won't let them keep the "big lie" alive......
We won't give up....or else the rotationalists win

We'll keep up the good fight....."The truth will out"


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## mward (Apr 7, 2004)

Ah yes, proof by majority. Very similar to proof by fire. Like this:

Galileo : there are planets and they go around the sun and the earth is not the center of the universe!
Church : *Burns Galileo's feet*
Galileo : Nevermind!


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## B R H (Jan 13, 2004)

*Why do you need to see math for something that is*

so plainly obvious to feel? The only reason I feel the need to even speak up on the subject is that I can't stand it when arrogant engineers or mathematicians claim to have all the answers yet their solutions don't yield results that are in line with common sense or experience. I don't have all the answers either, but I know what I can feel and measure with a stopwatch.

If you don't like the experiment asking you to hold the wheel in your hand because it fails to consider that the leverage provided by the handlebars considerably reduces the effect, that's fine and true, yet nobody brought this up. That's because those models don't consider this. Do the experiment again with the bike in the stand and turn your bars. Again, I'm not saying these effects are so large as to make an amateur turn pro, but they are indeed large enough to concentrate on these areas first.

Don't think for a second that pros like light wheels for the measly 1 or 2 second savings those models will _prove_ they can save. Anybody who races knows that 1 or 2 seconds has very little to do with the end result in a race. It's more about how much energy you _saved_ during a race to get those 1 or 2 seconds at the finish line! Now have fun tellimg me exactly how much that is please even though you know there would be no way to show whether or not the numbers are accurate or meaningful.

Personally I have no real interest in the math anymore, but I am glad that some people do. I'm sure it will help them solve lots of important problems during their careers (seriously). However, you may want to try to be more modest about your claims. If you can't do that now, be prepared to do it once you are working in the real world. You just may find yourself saying "oh yeah, I forgot about" alot more than you think!


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## B R H (Jan 13, 2004)

But your proof isn't really proof at all without experimental data that matches up with the math now is it? You said it yourself when you mentioned "valid controlled testing". I agree that this is something that is really missing and also something that is very very difficult to produce. Fortunately this is one case where I personally don't need to see those results to be convinced.

I do agree that any number over somewhere in the neighborhoood of 2 times energy savings is absurd but I suspect a number around 1.1 is also off the mark. I also think your .01 could be off by a factor of 10! Anyway, I actually don't really care about the real numbers. I just don't want to see people swayed away from making rotational upgrades as a first priority. I have yet to see anyone unhappy with the results of weight savings in that area (bald tires being one exception!).

By the way, I can't recall ever having a shop try to sell me something because it's lighter. Around here the opposite seems to be true. If you are interested in something lighter, you are assumed to be a poser because everybody knows that only well recognized and well marketed and mass produced (i.e. usually heavy) parts are what truly fast people ride!

Now I can't wait to see the look on my wife's face this weekend at the end of a long climb on her new 2.3 WeirWolfs.


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## B R H (Jan 13, 2004)

*PS. "Rotationalists"... I like that.*

I think you've coined a term that will go down in history!


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## old_dude (Jan 27, 2004)

*Unsprung weight?*



fonseca said:


> I can feel just a 100g difference in tires. Heck, I can easily feel the difference between my DH tubes and my Specialized thin tubes. When I rebuilt my spare wheelset last week I was reaching into a bag of brass and al nipples and selecting the brass ones by weight in my palm. You don't have to believe me. I'm not a gram counter at all, my Titus Switchblade is pushing 30lbs, and that's my primary XC bike.
> 
> Most of my riding has lots of short, steep hills, where I am out of the saddle hammering all the way up. That's acceleration/deceleration at it's most apparent. Light tires and rims make a big difference in how easy it is to get to the top.
> 
> ...


Just a thought.

The weight removed from wheels is unsprung weight. Every time you hit a trail surface irregularity, the wheel will move up as the shock compresses. A lighter wheel should accelerate more quickly out of the way of the bump, and so offer less resistance to trail irregularities.

old_dude


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## rapwithtom (Feb 26, 2004)

*Physics Show-Offs*

OK most people here probably understand the physics behind analytic cycling....but y'all are forgetting some of the assumptions that are probably made in their models:

a) *surface roughness*. The model surely assumes that the roads are flat. I am not talking about surface or rolling resistance here (although I agree with Chester that this is probably the dominating factor anyway) but rather how much the wheel must vibrate up and down, and at what frequency (read: rocks, roots, whoop-tee-doos, bumps, etc.). For suspended wheels that are somewhat independent of the bike frame, clearly wheel mass is more important than bike frame or body mass in terms of the work required to keep the bike & body mass moving at a constant speed forward speed.

b) *directional changes. * Y'all seem to be focused on speed when talking about the energy cost of wheel mass acceleration. But also there is constant changing of trail pitch (up/down) and direction. Also, what about the work done by your arms in turning in simply turning the handle bars? Clearly heavier wheels have more rotational momentum and therefore require more work over the course of a ride.

These factors are not model-able from a practical perspective, but they attest to the fact that wheel mass is more significant than non-wheel mass. They may be second or third order effects, but over the course of a 2 or 3 hour hard ride, there probably is a significant difference in effort and/or fatigue (at least that is what all of us weight weenies _want _ to believe!).

Now, whether or not expensive wheels are an economical use of your $$$ surely depends on how many $$$ you have and how important it is to you to make your bike (very) marginally faster.


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## mward (Apr 7, 2004)

At the risk of reviving this .. (And I'm in my cups, so forgive me)

Dudes, it's the tires! I weighed out some new wheels I got that are extremely fast. Bontrager racelights with Kenda ... those 345 g kendas. They fly, they are like atomic wheels. I am so much faster on them. Well, I weighed the wheels themselves tonight, and they're heavier than my race wheels, which have Conti Explorer pros on em. Wtf? It's the wheels? Nope, it's the tires. Of couse, those kendas grip like .. well not like conti explorers, but Nino says those NBX's are happening. I'll try em after I get done trying the Kenda Karmas which are on the way from the LBS.

Get some light tires, the difference is amazing.


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