Originally Posted by
Leisesturm
A cyclist short enough to find 130mm cranks interesting is also short enough so that 170mm cranks will NOT cause their knees to hit their chests the way a taller riders knees would. Speaking of knees, the shorter crank represents a shorter lever to act on the forces presented by the combination of drivetrain ratio and wheel size. For the same gear, the forces at the cyclists knee will increase as the crank gets shorter. Period! Simple Archimedian physics. Nothing about the cyclists body structure can change this. Tendons, cartilage, and ligaments differ in their capacity for abuse, but I can wonder aloud about the long term viability of using the same gears as cyclists using "normal" length cranks when one has, for whatever reason, chosen to adopt significantly shorter ones.
I agree but I wonder: does it damage our knees more or less or the same when maximum pressure is achieved with the knees up towards the chest or when our legs are not terribly bent? In other words, does the range of motion affect the wear on our knees? I really don't know, and I wonder if it has been studied. Reading this thread makes me think that shorter cranks might be good for me. I've done a small amount of experimentation, and that has strengthened my theory, but I don't claim to know for sure.
I for one strongly suspect that the riders using short cranks instinctively stay in lower gears except when the usual opportunities to use bigger gears present themselves: tailwinds, down-grades, drafting tractor trailer rigs... what that means in the real world, is that these cyclists are slower than other cyclists and therefore not as much fun to ride with.
I don't see any evidence of this, and I tend to doubt it. You can convince me if you have some evidence, even anecdotal.