[Squawk 8888]

Not perpetual motion, but regenerative braking. A compressor linked to the wheels would capture the energy and use it to accelerate, which could substantially reduce fuel consumption.

[chaos_5]

A compressor linked to the wheels would capture the energy and use it to accelerate, which could substantially reduce fuel consumption.

Problem is compressing air is a very poor way to store energy. Enthalpy and entropy losses are high. You are much better off using hydraulics and a spring loaded reservoir.