Originally Posted by
sced
kinetic energy = 1/2 mv^2. Ratio = 25^2/20^2 = 1.5625 more energy required to sustain speed.
Not quite. That's the difference in energy, or the amount of work required to go from 20mph to 25mph. This is different from the amount of power required to sustain that speed, which is what the rider needs to input in to the system to overcome losses like drag and friction.