For me at 5'11.5", but more importantly with a 77.5cm seat height, going from 172.5 down to 165mm was awesome. Going to 160mm was better still. 155mm was perhaps marginal gains, and 150mm I simply did not like. I would trial these on my fit bike, under thresholdish power, in aero position, multiple, multiple times.
Based on about 1500 fits done by guiding riders to the limits of their current crank before trying multiple shorter lengths, I've come up with a rough guide to get you in the ballpark. The vast majority of riders are self selecting something in these ranges:
<60cm seat height :: Crank 145mm or less. Really as short as you can find, maybe go custom. Iâ€™ve fit down to 135mm with custom cut BMX cranks.
60-65cm :: Crank length 140-150mm
65-70cm :: 145-155mm
70-75cm :: 150-160mm
75-80cm :: 155-165mm
80-85cm :: 160-170mm
>85cm :: 165-175mm Keep in mind that of the tallest and strongest professional athletes I have fit literally ZERO of them have preferred anything over 165mm. These are 6â€™3â€ť and taller athletes pushing wattage over 375 watts at threshold and upper 200s to 300 for IM races. "
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