Wheel bearing – what is it? When does it need replacing?

Do you hear a buzzing, rubbing, whining, humming or knocking noise from around the wheels while driving? These could be symptoms of a wheel bearing failure. The malfunction can even cause the wheel to lock up. How do you recognize a wheel bearing failure? What types of bearings are found in passenger cars? These questions are answered in the following article.


What is a wheel bearing?

To help you understand what a wheel bearing in a car is, you should first learn a little about its structure. So, in the bearing, there are balls or cones. These are placed under a metal housing and immersed in grease. This design has a great advantage. The balls and cones working in the grease hold the bearing element in position and ensure its rotation with minimal resistance. This is how the bearing, together with the hub, connects the car to the wheels.

The design of the bearings in the wheel can vary, but the function they perform is always the same. They hold the bearing component in position and allow it to rotate, while minimizing drag (through the use of reduced friction surfaces and lubrication).

Bearings are manufactured from strong materials that are resistant to temperature, pressure, friction, corrosion, etc. This should not surprise you. First, because the wheel bearing is subjected to really extreme overloads. Secondly, in this way, the manufacturer can maximize the life of this component. And durability is the key word here. In the case of cars, the wheel bearing, together with the hub, connects the car with the wheels and has to endure very high forces and loads. And moreover, it is largely responsible for driving safety.


Wheel bearing types

Classic cars had tapered roller wheel bearings, which require periodic adjustment. Nowadays, angular contact ball bearings are used in a closed design with no need for adjustment. Wheel bearings are divided into composite single-row or double-row - replaceable, integrated into the hub, or form an assembly. 

Older cars, such as the currently fashionable classics, used tapered roller wheel bearings. Their distinctive feature was that it was possible to separate the outer ring of the bearing from the inner ring (they do not have a closed structure). This has an obvious advantage. A damaged wheel bearing in such a case can even be reconditioned on its own. It is enough to replace the damaged rolling elements, and to lubricate the replacement parts. This restores the original performance and minimizes the cost of repair.

Unfortunately, wheel bearings of open design also have a disadvantage in the field of operation. Bearings of this type, require servicing. This involves lubricating them, as well as adjusting the clearance. This requires the removal of the component. Fortunately, technology has moved on, and modern wheel bearings do not require any service. Nowadays, angular contact ball bearings are used, operating in a non-removable closed system (composite bearings). They do not need servicing or adjustments. On the other hand, if they fail, they are replaced in their entirety. This can compound the cost of replacing a wheel bearing.


What are the two 2 types of bearings?

Two types of ball bearings are used in automobiles. Single-row ones carry heavy loads, but in one direction. Double-row ones carry radial and axial loads.

- Single-row composite bearings - can carry very heavy loads, but only in one direction. Single-row bearing rings have one high rim and one low rim, which allows the use of multiple balls.

- Double-row combined bearings - consist of two angular contact ball bearings, built in a diverging arrangement. These bearings are superior, as they can carry radial and axial loads.


What is the construction of a wheel bearing?

The wheel bearing in a car consists of:

- Outer treadmill (in simple terms - the outer part of the cylinder)

- Inner treadmill (inner part of the cylinder)

- Rows of rolling balls, made of steel

- Ball separators

- Dust cover

- Lithium grease

Depending on the wheel bearing used, the moving element can be either the inner race or the outer race (for example, when the bearing is integrated into a brake drum).


What bearings are used in car wheels?

In modern cars, composite double-row bearings are used. Even the most popular design of the wheel bearing requires further division into subtypes. There are three: replaceable (press-fit); integrated into the wheel hub (non-removable); and complete assembly (non-removable set of bearing, hub, knuckle, and ABS sensors).

- First-generation wheel bearing - a replaceable bearing, press-fitted into the wheel hub using a hydraulic press. The unit, enclosed in a single housing, consists of two wheel bearings with factory lubrication and a fixed preload. This type of bearing resembles a low cylinder with a hole in the center. It is sold complete with a crown nut and a metal ring.

- Second generation wheel bearing - a bearing integrated into the wheel hub. The whole component is non-removable - if the wheel bearing fails, the whole component must be replaced.

- Third-generation wheel bearing - a complete assembly (in most cases, not disassembled), consisting of a bearing, hub and knuckle. The inner hub is used to attach the brake disc and wheel, and the outer hub is part of the steering knuckle. The assemblies can be immediately integrated with the speed sensors of the ABS safety system (also used by ASR, ESP and the intermediate wheel pressure monitoring system, TPMS). Replacement of such a wheel bearing is simple – just tighten the bolts to the correct torque and connect the sensor plug. However, the cost of the entire component is high.


How long does a wheel bearing last?

Modern wheel bearings have a small diameter, are light, and do not require adjustment during operation. Therefore, they are characterized by very low maintenance and an extremely compact size. Unfortunately, such a design also entails some disadvantages. The life of a wheel bearing is determined to be about 85 to 100 thousand miles. Only after this time can the symptoms of a defective wheel bearing appear. In practice, however, it may be different. It happens that the components wear out faster. Then, however, a bad wheel bearing is signaled by the vehicle with a series of signals.


How do I know if a wheel bearing needs replacement?

- Buzzing – increasing with driving speed. Buzzing decreases in intensity after turning to one side, when only one of the wheel bearings is damaged. At this point, you should know that the noise in the wheel while driving is really intense. Sometimes it turns out to be loud enough to effectively drown out even the car audio.

- Friction at the beginning of the drive, which may disappear after a few kilometers. The symptoms of a damaged front-wheel bearing can be difficult to recognize. Sometimes drivers do not notice them.

- Very loud metallic sounds, which can be described as squeaking and whining (this often means a lack of lubricant and a seized wheel bearing).

- Noise and rattling while driving, a symptom of backlash and rolling ball damage.

As the failure of the wheel bearing progresses, the noise increases. After a few hundred kilometers, the wheel may become buried (in the absence of lubricant) or the bearing may break, which may even cause the wheel to break off.

How do I check the wear of the wheel bearing? In a situation where you notice a noise occurring while driving and increasing as the speed increases, try gently turning the steering wheel once to one side and once to the other. If, under the influence of this maneuver, the noise decreases, the symptoms will clearly indicate a worn wheel bearing. It is worthwhile to have such a diagnosis confirmed by a mechanic.


9 reasons for wheel bearing failure

A buzzing noise in a car can indicate that the wheel bearing is worn out. The formation of this damage can have very different reasons. Sometimes it's determined by natural wear and tear, and sometimes it's a mistake you make while driving your car every day. So check out the list below:

- Wear and tear - as we mentioned above, after 85,000 or 100,000 miles of mileage for good quality bearings and 30,000 miles for the cheapest replacements.

- Mechanical damage - such as hitting a wheel against a curb.

- Post-accident or post-collision mechanical damage like in many last sold vehicles (hitting the wheel).

- Improper, pseudo-sports car operation.

- Corrosion, resulting from improper installation.

- Poor installation of the wheel bearing - this happens when the replacement bearing is not installed using a press, but by substitute methods.

- The use of the wrong bearing for a given car model - especially a cheap replacement that does not have ideal dimensions but is only similar to the original.

- Too high a bearing temperature, resulting from poor, too-tight installation.

- Dislocated brake discs, causing whipping while driving.


Can I drive with a bad wheel bearing?

Wheel bearing malfunctions cause a significant reduction in driving comfort, as the buzzing can be so strong that it drowns out the car audio. It should be remembered that this is a very dangerous defect – in extreme cases, the wheel may jam while driving, leading to an accident. You should remember that the wheel bearing is a component that will wear out eventually. 

Real also:

A wheel bearing can wear out gradually, and it can also be damaged suddenly, either in a collision or an accident. Fortunately for the driver, the failure of a wheel bearing is signaled by a series of sounds that are impossible not to hear. The symptoms cannot be ignored. A damaged wheel bearing causes danger to you, your passengers and other road users.


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