Is there any advantage to changing the crank length on a tri bike (ie going from a 172.5->175)? Can this even be done considering the restriction of ground clearance?
In theory a longer crank gives more power due to a longer lever advantage but a shorter crank is better for high cadence.
To tell the truth, I can’t actually notice a difference of 2.5mm on cranks I’ve tried.
Ground clearance won’t be a problem.
I notice a big difference.
Have and had 175 on my mountain bike and 170 on my (triple) road bike. My tribike came with 172,5 and a double. I changed the crankes to 175 its like having another gear. Mountains are so much easier. I love the 175s. Its much easier to climb for me. Feels much more natural.
I will also change to 175 on my roadbike in the long run.
One of the recent articles just cited by Dr. Coggan might suggest that shorter cranks are better in some instances, because the energy expenditure of cycling is directly related to the speed of the intra-muscular contraction. (I hope he hasn’t left the board, so that he can better explain this, or correct me if I am stating this wrong). Longer cranks make your foot travel slightly faster, if you stay at the same rpm. If a little longer crank allows you to decrease your rpm while still maintaining an economical (for you) power output, then, the longer crank may be better for you.
One fellow I know that works with top-level riders bases his crankarm length on femur/lower leg length ratios. I don’t know if this is the best way to do it, but that’s what he does. He recommends me to ride a 172.5, I ride a 175. I can tell the difference in crankarm length when trying them out side by side, even being blinded to which length I’m on, but, I don’t know if either length is faster or slower for me…I’m guessing there wouldn’t be a difference…again, I don’t know.
"Dr. Coggan … (I hope he hasn’t left the board, "
He hasn’t posted here for eons. He seemed to get p*ssed off over one of the PC threads and disappeared. But he posts over on Gordo’s site fairly often.
Duh. OK you got me. Which thread?
It’s not the length of the crank, it’s… oh, never mind.
Bugunderrock/RipVanWinkle/TheChameleon/rotorcranker/not a PCer
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Optimal crank length is based solely on athlete preference. When somebody says, “I changed crank length and it was better,” then they’re right. It was better.
At the same time, when somebody says, “Heck, I can’t tell the difference,” then they are right as well.
Within the range of reasonableness (say, 165-180), there is no objective advantage to any given length, even for athletes of various bone lengths. Longer gives more leverage, but you move your feet through a bigger circle. Vice versa. It’s all just tradeoffs, like cadence and seat angle and all sorts of other things.
You just gotta choose what feels good to you. Generally, taller folks like longer cranks and shorter folks like shorter cranks. But, exceptions abound.
With some help from a friend I figured it out. But I’m not to swift sometimes. Thanks anyways Hid.
I read a story somewhere that “Big Mig” rode 180’s in the tours. Of course we know how he dominated the TT’s.