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Is it advantageous for a tall guy to use long cranks?(5 posts)

Is it advantageous for a tall guy to use long cranks?Groucho Marx
Aug 14, 2001 11:12 AM
Is it advantageous for someone with longer legs to use longer cranks? I'd imagine it would given the whole thing about torque. Or would you just get more tired moving your legs that much farther?

I was thinking how as the size in bike increases as the size of the rider does, the thing that stays the same is the diameter of the pedal stroke. If a larger rider used a larger crank arm, he would require relatively the same amount of biomechanical effort to move his leg around the pedal stroke as a smaller rider with a regualar crank arm. However, now that same force creates more torque. This kindof makes sense to me. Would this be any advantage?

I'm also pretty sure this is harder on the knees. So I'm not talking about extreme changes. Thanks.
It sounds logical...Bruno S
Aug 14, 2001 12:27 PM
If you think about it everybody talks about fit. Frames come in 1 to 2 cm increments, seats tilt and move front to back, the stem can be raised, etc. But then, for most bikes out of the LBS the cranks come in mostly 3 sizes. I have long legs (36 inch inseem) and recently bought 180mm cranks. There is no data to back up that longer is better but for me it made sense. Since I have been using the long cranks I feel that I have more power and I also feel that my knees hurt a bit after long rides. I say feel because I have no way to prove that the longer cranks are the reason I am riding faster now than ever. I also broke my frame from a chainstay. It could have been caused by the added torque of the long cranks.
Maybe, and maybe not.Kerry Irons
Aug 14, 2001 5:01 PM
You will find no high quality data to support any particular crank length as being better than any other. This is true whether or not you correct for leg length, femur length, etc. On the other hand, you will find lots of anecdotal or low quality data to support all kinds of conclusions, and more theories than you can shake a stick at. A rider's response to changes in crank length is 1) highly individual, 2) dependent on riding style and the event (TT, climbing, crits, track racing, etc.), and 3) most important, highly adaptive. This is why it is so hard to study the effect of crank length.

So the short answer is: if it feels better and measures faster, do it. If it doesn't feel better but measures faster, maybe you should do it and hope to adapt. And even if it doesn't measure faster, you may adapt and get faster. Simple, eh? NOTE: measures faster means repeat timed distances on different days in different weather, not just "faster on my nightly ride" which can mask the effects of weather, fatigue, and the placebo effect of riding on "faster" equipment.
Kerry's right.look271
Aug 14, 2001 5:19 PM
Everythingh I've ever read says that there is no good evidence to prove that changing crank arm lengths can change your speed. That said, I recently went from 170mm to 172.5 to 175. The jump from 170 to 172.5 was not really noticeable; the jump to 175 was. I like it, and I'm fairly tall (6 ft). Speed? I can't really say, I just like the way it feels. BTW; no problems w/ the knees.
I think about the angle of the knee joint.Spoke Wrench
Aug 15, 2001 5:34 AM
If you put a little kid on an adult crankset, their knees have to come up way high at the top of the stroke. That can't be good, can it? The opposite extreme, a long legged guy on a short stroke crank isn't as clear to me. I have a friend who is 6'7" who feels he has to pay extra for Dura Ace cranks because they come in 180mm length.

Fortunately, my height is right on the mean for males in the US so I don't have to spend too much time thinking about crank length.