Different cyclists have different leg lengths. It seems obvious that crank length should be proportional, so long legged cyclists should have long cranks, short-legged cyclists should have short cranks….and yet, 99.9% of adult bicycles have crank lengths between 165 and 175 mm. Have the bicycle manufacturers joined in a great conspiracy to force everybody to ride the same length cranks, regardless of their needs?
This is a common misunderstanding. The “leverage” of a bicycle drive train, also known as “gain ratio” depends on the crank length, wheel diameter and the sizes of both sprockets.
Yes, if you go to longer cranks without changing any of the other variables, you will have more “leverage”, which is another way of saying you’ll have a lower effective gear…but on a multi-speed bike, you can change gears at will!
Ay, there’s the rub! Assuming you adjust your gearing appropriately, crank length has no effect on leverage, it just has to do with the range of motion of the knee and hip joints.
S.Brown.