A pinion bearing is a mechanical element that constrains the movement of a pinion, a gear with a small number of teeth. Pinion bearings are a common part of automotive differentials. These are devices that allow cars to corner better by allowing connected wheels to rotate at different speeds.
Pinion bearings ensure that pinions only move in one direction, thus making the overall machine more efficient as no energy is lost on undesired movement. They also are designed to reduce friction in the direction of desirable movement, again increasing efficiency. In drive differentials found in cars, pinion bearings help the smallest gears in the differential work smoothly. Differentials are made up of a series of gears and cogs, and it is the smallest gears that allow one wheel to safely rotate faster than the other. Cars without differentials suffer strain on their axles when cornering, as the wheel on the outside of a turn naturally rotates more quickly than the one on the inside.