Originally Posted by
Sierra_rider
Here's an interesting video on the topic. It's not your average "Youtube bike fitter" vid that just talks about hip angles, this goes further and graphs angles as well as femur velocities, in relation to different crank length. Basically, the rate of acceleration of the femur, through the pedal stroke, increases with longer crank arms. The creator of the video posits that this is more taxing on joints as well as fast twitch muscle fibers. An argument could be made that both of those issues are of increased importance to older riders. Although, the ideal velocity and rate of acceleration of the femur, might not be the same for different femur lengths. I myself feel best on 172.5 or 175mm cranks, and can easily spin a 90-100 rpm cadence on them.
https://youtu.be/S0SpYdxg1UY?si=zdPF77oiQZTlpE8j
Makes sense. I'm more of a slow-twitch guy, which is part of what makes me think I might get some benefit from 165mm vs 170. Although it was a long time ago, I originally came to road cycling from a competitive bmx background, where I was using 175mm and and bmx is all about fast-twitch obviously. Going down to 170mm for road seemed 'about right' and the last time I had a professional bike fit 15ish years ago I got a head nod from the fitter. Hadn't put much if any more thought into it than that until recently.