Originally Posted by
San Rensho
Good analysis.
I agree there is lateral flexing in the frame. You can see this when you ride a trainer, the BB sways back and forth. And I agree that the lateral lateral force component does not contribute to making the pedals spin. But, if the frame were infinitely stiff, in other words, if it were impossible to make the BB sway back and forth, wouldn't the frame prevent the pedalling force from being applied laterally, and therefore all of the pedalling force would be used to spin the cranks and none would go in a lateral direction and be wasted?
Yeah, all the force would go directly to the wheel (assuming infinitely stiff drivetrain components), but the force used to flex a frame is not wasted -- it goes back to the wheel when the frame unwinds (see my trainer demonstration above).