Crank Arm Length

mattsull

This is a topic that I have overlooked through the purchase of several bikes. I recently went in for a fit on a road bike I just got and the fitter was surprised I had 175mm cranks. They came with the bike which I bought used. Anyway, it got me thinking. I found the following article that suggests I should use a 170mm based on my inseam length and bike frame size. I wanted to get folks opinion on this. What are the performance implications of riding a crank arm that is too long? What about power output? etc . . .  This could be my excuse to purchase a Quarq with shorter crank arms.

www.cptips.com/crnklth.htm

Just found this too.

www.slowtwitch.com/Tech/Crank_arm_l...i_727.html

kjanracing

I have about a 32" inseam. I've been on 172.5mm cranks for years. I ran 165's on the track to hit the high rpm's necessary for that type of racing. I FEEL like I don't get enough oomph on 170's especially when climbing. The 172.5s feel just right, but I've been on them longest. I feel like I get more power out of 175's but I'm not as smooth with them. I do run 175's on the tandem and mountian bike,those seem to be more torquey type rides, but I'm less able to spin them. Really, if someone swapped out the 172.5's for 175's and I didn't know it, I'm not sure I could tell.

Norton

Lots of discussion over on Slowtwitch regarding crank length and the benefits of reeeeealy short cranks for the aero position. Like 145mm as the optimum!

tim cronk

Great topic. One I became interested in due to being in the market for a quarq. Currently 5'6" with 30" inseam riding a small QR I think its a 51cm frame with 170's. It would appear to be a no brainer for me to at least go to 165's. Its also a no brainer for reduction in knee stress. The real question though is what is optimal length. Lot's of guys much larger than I are moving to 165's and there is a guy on ST saying 145's???? One of those things the more I read the more complicated it gets. More than likely I will get 165's on my Quarq when I bite the bullet . Nice links posted and good luck Matt.

Nemo Brauch

145? Is there really such an animal?

I'm 5'2" (well, almost) and Todd from TTBikefit recommended I get 165s for optimal fit. At the time, finding 165's was tough enough, I don't know where you go to find anything smaller! Kids bike?

kjanracing

Probably not Quarqable but daVinci Designs makes cranks down to 150mm. Nice cranks! Have them on my tandem, and cross bike. http://www.davincitandems.com/comp.html#cranks

tim cronk

The PowerCranks guy actually makes adjustable cranks I think from 145-185. If this wasnt confusing enough there is a new thread on ST compact vs standard which seems to support the theory most people would be better off with compact. Arggg my head is spinning!