The crown and pinion assembly in a vehicle is a set of two perpendicular gears, the crown-wheel and pinion, that regulate the amount of torque applied to the car's wheels. Together they are responsible for transferring power from the engine's main drive shaft to the gearbox's differential system.
The main role of the crown and pinion assembly is to regulate the amount of power applied to each wheel via the car's differential system. A differential system allows the power distributed by the engine through the drive shaft to be dispersed unevenly, creating safer and more comfortable turning conditions. When turning to the left, for example, the differential sends more power to the rear wheel on the right side of the vehicle. Because the right wheel must travel farther than the left wheel does during a left turn, the crown and pinion are responsible for making the right rear wheel travel slightly faster to cover the extra ground it must make up.
Crown-wheels and pinions may be replaced or swapped for one another to affect the power output of a vehicle. Local auto repair shop sell a variety of crown and pinion sets. Websites such as Quafie.com also offer a range of crown and pinion assemblies that may be purchased to suit a breadth of performance demands.