Wheel Bearings: The Hum You Shouldn't Ignore

A low hum or growl that rises with speed is one of the most common sounds drivers learn to tune out. Very often it is a wheel bearing wearing out. Bearings rarely fail all at once, so catching the problem early can save you money and keep a minor repair from becoming a safety issue.

What a wheel bearing does

Each wheel spins on a set of steel balls or rollers held in a sealed race. That assembly, the wheel bearing, lets the wheel rotate smoothly while supporting the weight of the car. On many modern vehicles the bearing is part of a hub assembly that also holds the wheel studs and, often, the wheel speed sensor used by the anti-lock brakes and stability control.

Bearings are sealed and packed with grease at the factory. They are designed to last a long time, but water, dirt, heat and impacts can wear them out early.

Signs of a failing wheel bearing

Watch and listen for:

• A humming, growling or roaring noise that gets louder as you speed up
• A noise that changes when you turn or change lanes, as weight shifts from one side to the other
• Grinding or clicking from one corner of the car
• Looseness or play in the wheel, sometimes felt as vague steering
• Vibration through the steering wheel or floor
• An ABS or traction control warning light, since a damaged hub can affect the wheel speed sensor
• Uneven tire wear on one wheel

Bearing noise is often mistaken for tire noise. Tire noise typically changes with road surface, while bearing noise tends to change with speed and cornering load.

Why you should not wait

A worn bearing usually gets louder gradually, so it is tempting to put off the repair. The risk is that as the bearing deteriorates, heat and play increase. In severe cases, a bearing can seize or allow the wheel to wobble, which affects steering and braking. Excess play can also wear out brake rotors, pads and the CV joint faster.

If the noise is getting worse, or you feel looseness in the wheel, get it inspected soon.

Common causes of early failure

Bearings can wear out from age and mileage, but some things speed it up:

1. Hitting potholes and curbs. Hard impacts can damage the races inside the bearing.
2. Water intrusion. Driving through deep water can push moisture past the seals.
3. Improper installation. Using the wrong tools or over-tightening can damage a new bearing.
4. Oversized wheels and tires. Larger, heavier wheels and lower-profile tires can put extra stress on bearings.
5. Worn related parts. Bad suspension components can shift loads onto the bearing.

What the repair involves

A mechanic will usually confirm a bad bearing by test driving the car, lifting it and checking each wheel for play and roughness. Some shops use listening tools to pinpoint which corner is the source.

On many cars, the repair means replacing a bolt-in hub assembly. On others, the old bearing must be pressed out of the steering knuckle and a new one pressed in, which takes more labor. Some mechanics recommend replacing bearings in pairs on the same axle, though that depends on the car and the condition of the other side.

Costs vary widely depending on the design, labor time and whether the hub includes an integrated sensor. Ask for an estimate that lists parts and labor separately.

How warranty coverage treats wheel bearings

Under a factory bumper-to-bumper warranty, a defective wheel bearing is often covered, while damage from impacts or neglect generally is not. Factory powertrain warranties usually do not cover wheel bearings unless they are part of the drive axle assembly, and that varies by brand.

With vehicle service contracts, coverage depends on the plan level. Bearings may appear under suspension, drive axle or a general list of covered parts. On a named-component plan, check whether front and rear wheel bearings are specifically listed. On an exclusionary plan, check that bearings are not on the exclusions list.

Also note any conditions, such as exclusions for damage from road hazards, lifted suspensions or aftermarket wheels.

How Warranty Wizards can help

We help you compare plans from third-party providers and show you exactly where parts like wheel bearings fall in each contract. For a free quote and a clear explanation of coverage, visit /get-a-quote/.