sentences:  The motive output is then sent down a shaft to a differential in the centre of the car, which in the case of an M4 layout, distributes power to both front and rear axles.The "rear-engine, four-wheel drive" layout (abbreviated as R4) places the engine at the rear of the vehicle, and drives all four wheels.This layout is typically chosen to improve the traction or the handling of existing vehicle designs using the rear-engine, rear-wheel-drive layout (RR).