Cycle Efficiency vs. Cycle Resistance
Bicycles are mechanical. They have chains and gears and pedals, which interact in the process of riding. As with all machines, when parts work together, they create heat which is lost. This friction has a net effect of reducing the amount of pedal force that is translated into rear wheel forward force.
Modeling Cycle Resistance
In this context, some of the pedal force simply does not make it in one form or another to the rear wheel. Fortunately, bicycles are highly efficient and this loss is of the order of 5% or less. It is often approximated by reducing the pedal force by a percentage.
Next Topic: Cycling Resistance Efficiencies