Originally Posted by
Leisesturm
Shorter cranks don't reduce your power, they decimate your power. Unless you are a trained cyclist that is used to cadences up to and exceeding 100rpm. Most regular cyclists find cadences over 80RPM mentally fatiguing even if not physically so. As to frames properly designed to use short cranks... which would those be? All production frames assume the use of cranks considered "normal". That would be around 165mm on the short end and 175mm on the long end. Not that stops anyone from using shorter or longer cranks as they see fit. As I understand it, a slack seat tube, set back seat post configuration emphasizes low rpm torque, and such a configuration assumes the use of longer, not shorter crank lengths. The ultimate and polar opposite configuration would be a track bike. If you can describe a lower and more aerodynamic position than a 75* seat tube angle track bike with a -15* stem and Pista bars I'd like to see it. Swap out the Pista bars for Triatholon bars and you can maintain that low, aero position more or less comfortably for hours.
Sorry, your wrong. Some basics.
Power = torque x rpm.
Longer cranks may increase your torque, just when your cranks are level, but then reduce your torque when you are trying to get through top dead centre. Longer cranks increase the degree of movement that your leg needs to go through in the whole cycle making you less efficient.
Shorter cranks may reduce your maximum torque when the cranks are level but make it FAR easier to get through top dead centre giving you more torque in the TDC position than if you had longer cranks.. Shorter cranks reduce the degree of movement in you legs making you more efficient, particularly if you have your seat positioned correctly.
Shorter cranks smooth out your torque delivery and allow you to spin higher cadences, giving you just as much power, as longer cranks. Short people who are struggling to deal with cranks that are really too long for them will produce more power with shorter cranks. If your tall and you fiddling around with 5-10mm crank length differences that it might not matter to you.
EDIT; I don't have any problems with high cadences. I find 90rpm to be very relaxing. 110-120rpm is fine if I'm working hard and I get to over 140rpm in a sprint. I don't have to think about it at all.
Anthony