Originally Posted by
Iride01
Radius is only half the picture. You have to address the total diameter. So a 5 mm change in crank length means your stroke is 10 mm more, which is .394" or a little more than 3/8ths inch.
Surprisingly for me, the difference was noticeable when I went from 165 mm to 170 mm cranks. YRMV.
As for those that think shorter cranks mean harder pedaling, then they are forgetting to shift down to a lower ratio gear combo.
Since I'm a road bike type and do get in the drops fairly often, I don't need my knees driven an inch further into my chest by using the 190 mm cranks. I'll keep my 165's and be assured that I can pedal while turning without hitting the pavement.
So to me, it still gets back to whether you want to be a masher or a spinner. No formula needed.
Well I don't know about shifting down, but I think the harder pedaling is a big "so what". None of our pedaling is all that "hard", not like leg presses, and to the extent that you'd think it was, that 5mm represents only 3% difference in torque.
What really limits us - relative to the difficulty of exertion - is the power requirement. Which is the same for either crank length. Neither this, or the cadence as a lot of people think, are really considerations for or against changing the crank length. It's more about, perhaps only about, the change in the range of motion.