Originally Posted by
RChung
That's the force (torque)
produced by the rider. The question is why would less force be
required during different parts of the pedal stroke, i.e. why would the external forces (rolling resistance, aero drag, etc.) vary with pedal position.
I suspect the difference is that the force required is closer to constant throughout the circle of the pedal stroke whereas without a headwind, you can apply less force in the dead parts of the stroke.