Your car’s wheels spin around a stationary axle, and in order for them to do so, something has to allow for “slip” between the two. That something is a wheel bearing.

A vehicle’s wheel bolts to a hub, and the wheel bearing (there may be an inner and an outer) is in the center of that hub. Wheel bearings vary in size and come in many different styles, but a common trait is that they use either small balls or cylindrical rollers that roll between two smooth metal rings: one on the outside that fits into the hub, the other on the inside that fits around the axle. In some cases, the bearing assembly also has side plates that seal the necessary grease inside.

A wheel bearing leads a tough life. The balls or rollers inside them can be about the size of the diameter of a pencil or AA battery, and there might be a 12-20 or so around the circumference of the bearing. Each bearing (or pair of bearings) at each wheel has to support the entire weight of that corner of the car. Furthermore, the wheel turns quickly at high road speeds, making for a lot of potential wear inside the bearing.

Although it’s not uncommon for wheel bearings to last up to 100,000 miles, they eventually go bad. “Natural causes” would include normal wear on the balls or rollers, or grease eventually leaking out through the seals that hastens wear. The life of a wheel bearing also can be shortened by sharp blows, such as the wheel hitting a pothole, as well as water seeping past the seals and diluting the grease or by sand or salt that likewise finds its way past the seals and causes premature wear.

Telltale Signs of a Bad Wheel Bearing

Noise is the most obvious indicator of a bad wheel bearing. Sometimes it announces itself with a howling or grinding sound that increases steadily with speed. It may also be noticed in corners or when you quickly move the steering wheel back and forth while driving straight ahead, as the weight that shifts onto or off of a bad wheel bearing will change the sound it makes.

Another sign could be play or vibration felt through the steering wheel due to the worn balls or rollers shifting around inside the bearing. This degradation would likely be gradual, getting slowly worse over a relatively long period of time and making it difficult to sense. However, it could eventually cause the antilock braking system light to illuminate due to misalignment between two of the system’s components; that would be more noticeable.

A Good Way to Check for a Bad Wheel Bearing

If you or a mechanic can raise the car off the ground by the frame or a suspension component — thereby allowing the wheel and tire to rotate freely — you can often determine if a wheel bearing is bad by grabbing onto the sides of the tire and pulling it in and out or pivoting it side to side. Looseness in any direction indicates a bearing going bad. Also, spinning the tire may produce a noise indicative of a worn bearing.

What Can Happen With a Bad Wheel Bearing?

A bad wheel bearing can lead to bad things. For one, the bearing can seize, which would quickly slow the wheel or even lock it up, preventing it from turning. This can cause a loss of control, especially if it happens when you’re driving at faster speeds. The bearing could also break apart, which might cause the wheel to fall off — likewise causing a loss of control regardless of speed.

There is a bright side, however: Usually the wheel bearing will give ample warning before it fails. You only have to recognize its cries for help.