Originally Posted by Ideologue
I read that the maximum amount of torque momentarily produced by a professional (racing) cyclist is in the region of 1,000 Inch Pounds. That is 83.3r Foot Pounds, or 112.984 829 333 Newton Meters.
A 250cc motorcycle I used to ride only produced around 20 Newton Meters, so is the 112+Nm figure really an accurate one for the maximum torque a human can produce on a bicycle? It seems rather high to me. But then considering a rider with a mass of around 100kg standing up on the pedals and allowing his entire weight to push down on 175mm cranks (with a turning circle of 1099.6mm). This rider without even trying, and merely allowing gravity to pull his mass down and turning the cranks in the process, will exert approximately 539.35Nm of force through the bottom bracket spindle.
What do you make of this?
Well, it's really pretty simple. Your motorcycle produced 20 NM, but it did it at 7500 RPM, while the human produced it at 75 RPM. To get 75 RPM out of the motorcycle, you'd need to gear it down 100:1, and that would multiply the torque by 100, giving you 2000 NM.
That's why higher RPMs are sought after in engine design. If you can double the RPM range of an engine without lowering the torque (you can't, but bear with me..., then you could gear the engine down 2:1 and get double the torque.