Wheel bearing are one of the most crucial components of a car's suspension. They are usually located in the hub (the part that the brakes and wheels are attached to) or even the brake drum or rotor itself. Wheel bearings allow the wheel to rotate freely as the car travels down the road. Most cars have an inner and an outer bearing on each wheel.

A wheel bearing is a simple device made up of two main components, the bearing itself and the race. The bearing itself consists of a metal housing that is pressed over a row of ball bearings that circle the metal housing. These ball bearings in turn ride on the race, which is a very smooth metal surface. When a wheel is rolling, the action of the ball bearings rolling against the surface of the hub that allows the wheel to spin smoothly