Based on a force inputed in a machine, how do you calculate the force outputed? I would have thought you could do this with a simple torque balance but this does not always appear to be the case. For example in the case of an accelerating bicycle, the force applied to the rear gear is Ft, but the force the bicycle applies on the ground is not Ft*(Rg/Rw) but slightly less than that. Rg is the radius of the rear gear and Rw is the radius of the rear wheel. So it appears the output torque seems to lag slightly behind the input torque. Is this always the case?