General
Gearboxes. The differential

The driving force of a vehicle is generated by the tire's contact with the ground. A drive wheel therefore has two functions:

• a steering function like all the vehicle's wheels (4 in the case of a passenger car);

• a propulsion (or traction) function on one or more wheels.

There are several cases to consider.

• Propulsion is via a wheel, as in the case of motorcycles and tricycles. The force is in the vehicle's median plane, which of course contains the center of gravity. The force is therefore perfectly neutral with regard to stability.

• If we wish to have only one drive wheel on a 4-wheeled vehicle, this effort cannot be in the vehicle's plane of symmetry, and therefore imposes on the vehicle a rotational torque around a vertical axis passing through its center of gravity....