The ratio of kinetic energy to power required to maintain speed means that it is not worth it.
At the legal speed limit of 20 MPH, which is 9 meters per second, a 100 kg bike/rider combination has 1/2 x 100 kg x (9 m/s)2 = 4050 kgm2/s2 = 4050 J1/2 x 100� x (9�/�)2 = 4050��2/�2 = 4050� kinetic energy.
To maintain this speed, about 200 W is needed on a drop-bar road bike on level ground; 300 W may be needed for CdA and Crr, both of which are about 50% higher with an upright seating position and the heavier tires common on electric bikes.
The 4050J will travel 396 feet in 13.5 seconds at 20 mph.
Regenerative braking is useful in cars because of higher cross-sectional density and better aerodynamics, and it generates more run time by storing kinetic energy in the battery.
