Branko D

He doesn't have proof that exactly 21% which he now advocates and sells, or 21.3%, is optimal, either. The few actual studies published on the topic which put trained cyclists on cranks of various lengths and found a small decrease in sustainable power only at extreme crank sizes. It's worth also keeping in mind that he sells people custom frames because extra long cranks on a mass produced frame which is designed for 170-175mm cranks reduce pedal clearance and change the handling.

The problem which is alluded to is, even if we agree taller cyclists would benefit from longer cranks in principle, the question is how do you get the ideal number. The numbers given by Zinn such as 21% and 21.3% suggest that I should be riding 175mm or 177.5mm cranks. 177.5mm? Yeah, no thanks!

​​​​Personally, when I was replacing a 175mm crankset with one with a power meter on one of my bikes, I went with 170mm cranks and the comfort is slightly better. I sometimes ride a bike attached to our turbo trainer with 172.5mm cranks and I can't say I produce any more or less power on it.

So, why not 20.4%? Or any other number in that range? Why not a range, say 20%-21%? Putting a precise number to it suggests that it's an exact science, and there is just nothing of the sort in it.

Anyway, on topic, within the confines of mass produced bikes and cranks (which, if you fall within 99% of the population height wise are appropriate for you), crank length doesn't have a meaningful impact on gearing selection.