Driveline / Tech / Tech Articles / Wheels & Tires

What is a Wheel Bearing & How Can You Tell if Yours is Going Bad?

We had to replace a bad wheel bearing/hub assembly recently, which gave us a good reason to write this article. (Image/OnAllCylinders)

A wheel bearing has a real simple job: It makes sure that your wheel spins freely, without any binding or vibration. A wheel bearing’s goal is to mitigate the effects of friction, which ultimately improves your car’s ability to roll smoothly—all while reducing wear to ensure it’s able to do so for a long time.

A wheel bearing is typically composed of a series of small roller bearings arranged in a circle and encased in a durable shell. The assembly is packed in grease and sealed to prevent excessive moisture and grit ingress. Then, the whole thing slips around the vehicle’s axle or spindle, where it can spin right round, baby.

Here’s a standalone shot of a Timken wheel bearing. But in many cases, bearings are often pressed-in to a hub assembly to be replaced as a single unit (like in the picture at the top of this article). Note the series of smaller roller bearings inside the main wheel bearing. (Image/Timken)

But given the amount of times it has to keep the wheels spinning really, really fast (and the rain-, dust-, and salt-rich environment it often has to work in), a wheel bearing will eventually wear out. While a failed wheel bearing can be a big problem, the good news is, it’ll probably give you plenty of warning that it’s going bad—you just have to know what to listen for.

How to Tell if Your Wheel Bearing is Bad

The key word above is “listen.” Though you may be able to jack-up your vehicle and check the wheel for movement and play, noise will typically be your first (and best) indicator that you’ve got a wheel bearing on its way out.

It’s always a challenge to describe a noise in text, but a bad wheel bearing will often start out as a “growl,” sort of like a dull, soft grinding noise. It can also be a whine, a hum, or a soft roar. In some cases, bad wheel bearing noise could even manifest as a clunk or squeak.

You may also start to feel it through your steering wheel or in your backside seismograph. Again, a wheel bearing’s job is to ensure your wheel spins smoothly. When it doesn’t, you’ll probably start sensing unpleasant vibration and noise throughout the passenger cabin.

The noise/vibration might only be noticeable at certain speeds, and it may even go away momentarily depending on chassis movement (more on that in a sec). In any event, it’ll likely get worse as the bearing continues its progression towards complete failure, so it’s good that you catch it as early as possible.

Here’s a close up look at our old wheel bearing pressed into the hub assembly. While it’s covered by a dust cap on the hub, ambient air, grit, and moisture can still find a way inside. You can see the roller bearings covered in grease around the bearing’s outer race. This particular bearing endured a nasty mix of road salt and ocean air for several years before checking out. Bravo. (Image/OnAllCylinders)

Avoid a Wrong Wheel Bearing Diagnosis

But before you point the finger at a wheel bearing, you want to make sure the noise isn’t coming from somewhere else. So here are a few things to consider:

  • Make sure your tires are in good shape and properly inflated. Worn, unbalanced, and underinflated tires can mimic the symptoms of a bad wheel bearing.
  • Does the noise change when you apply the brakes? Does it stop entirely? Then it’s a good idea to check out your drums/discs first, before going much deeper. In a safe area(!), experiment with some light brake taps, a few hard jabs, and then ride the brakes a bit to see if it affects the noise you’re experiencing.
  • Does the noise change with engine speed? Remembering that engine speed and wheel speed often change together, try this: While coasting to a stop on a highway off-ramp, (again, in safe conditions!) shift into neutral. If, when the engine RPM drops, there’s no change in the noise, then the noise is probably linked to wheel speed, which points to a wheel bearing problem. (Once you’re stopped after the test, shift back into drive and be on your way.)

We’ve got a really good article on driveline noises that goes into more detail. Check it out here: Quick Guide to Diagnosing Differential & Driveline Noises

How to Track Down a Bad Wheel Bearing

Now that you know what to listen for. You need to know where to listen for it.

Since a wheel bearing is located at or near the wheel, the noise will probably be coming from one corner of your vehicle—provided you’ve only got one bad bearing, of course.

It’s usually pretty easy to determine if the noise is coming from the front or back, given the driver’s seating position and their proximity to the front wheels. The hard part is often determining whether the noise is coming from the left or right (driver or passenger) side of the vehicle.

But good news there, as there’s an easy test that may help. While it’s not 100% foolproof, if you notice the noise stops while you’re turning—or even slightly veering—then an opposite side wheel bearing is the likely culprit.

Here’s a good illustration of the left/right wheel bearing diagnostic process we made using our state-of-the-art rendering software. (Image/OnAllCylinders)

That’s because turning shifts the weight off the side of the particular offending wheel. Now unloaded with less stress, the bearing might shut up for a second and be perfectly content. When the vehicle weight shift returns to normal, the bearing is back to being loaded and it’ll start to whine again (sometimes literally).

So pay special attention while turning and, at highway speeds, if you can safely(!) rock the steering wheel slightly left and right to shift the vehicle’s weight to each side, it may further help you diagnose where the noise is coming from.

Again, this isn’t a 100% accurate test, but it can be a big help.

As alluded to earlier, we had a wheel bearing go out on a front-wheel drive vehicle. Using the processes outlined in this article, we narrowed it down to the rear driver side wheel bearing. That was good news for us, as the replacement job was pretty easy and didn’t cost a whole lot either. This is the new hub/bearing assembly on the spindle, right before we torqued everything down and bent the axle nut flange to keep it in place. (Image/OnAllCylinders)

How Long Should A Wheel Bearing Last?

That’s a tough question to answer with a definitive mile threshold. We hear tell of wheel bearings lasting the life of the vehicle, like 200,000 miles and up. Conversely, some cars (cough*old Subarus*cough) seem to go through wheel bearings every few years or so.

It often boils down to both the vehicle and the driving conditions. All-wheel-drive cars put different demands on wheel bearings than, say, front wheel drive cars. Late-model performance cars place stresses on wheel bearings that regular commuter cars don’t. Mud-slinging off-roaders subject their wheel bearings to muck and grit that a street-driven car rarely sees. Make sense?

A big key to wheel bearing longevity is proper installation. Before putting the new wheel bearing back on, we cleaned everything thoroughly, as an errant bit of grit or a few rust flakes could easily shorten bearing lifespan. Here, we’re dousing the spindle with some brake cleaner prior to some deeper scrubbing. (Image/OnAllCylinders)

The takeaway here is that early detection is important. And narrowing it down to the precise wheel can help save you some time and money in diagnostic costs.

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2 Comments

  1. Also you can check a bad bearing buy taking off the grease caps then taking on a short run. Stop the car and with a thermometer point it at the centre of the bearing both sides of the car.The hottest bearing is the most worn and will give the loudest noises.

    • Very, very good point–we’ve even seen folks pinpoint a trailer bearing that was physically hot to the touch. Heat’s a key byproduct of friction, so it’s often a telltale sign of a bad bearing.

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