A wheel bearing is exactly what it sounds like: a bearing for a wheel. What's a bearing? It's an arrangement of steel balls, held together by a metal ring called a race. There are a wide range of styles of direction yet they are all fundamentally the same as and all do likewise work: they assist something turn with next to no rubbing. Like a wheel, a turbine, or a fair ride.
On a car, a wheel bearing is a set of ball bearings that support the wheel and ride on a metal shaft called an axle shaft. The wheel bearing fits tightly inside the hub, the hollow chunk of metal at the center of your wheel, which holds the lug bolts that you use to bolt your tire onto the wheel. The wheel bearing is pressed into the hub, from the back side of the hub.
What Does a Wheel Bearing Do?
Wheel bearings are used on all kinds of vehicles from bicycles to aircraft, and they all perform the same job: they allow the wheel to spin freely. Most wheel bearings are hardened steel and will withstand a lot of abuse. A wheel bearing's worst two enemies are heat and water. Heat caused by lack of lubrication can destroy a wheel bearing. Water that penetrates a sealed bearing will also destroy it.
Most wheel bearings manufactured today are sealed bearings. They come from the factory pressed together as an assembly: front race, bearing set, center race, bearing set, and outer race, with seals on both the front and rear race. Seals protect bearings from the elements, water, and debris, and they also also seal in the high-temperature grease the bearing needs. When the seal is broken or damaged, the wheel bearing will fail and start making noise.
What Kind of Noises Do Wheel Bearings Make?
When the seal on the wheel bearing is broken or damaged, the noise starts out very faint and becomes louder over time. Within a month, it will be very noticeable, increasing at higher speeds.
The noise is something like the noise that your tires make when hitting a rumble strip on the highway, just not quite as loud: a rhythmic rotating noise. It's something like the sound of playing cards flapping against your your bicycle spokes.