What is another name for a wheel hub?

Common alternative terms for a wheel hub include "hub" and, in automotive repair and parts sales, sometimes "wheel hub assembly." However, strictly speaking, a wheel hub and a wheel hub assembly are not exactly the same thing. Likewise, a wheel bearing should not be used as an exact synonym for a wheel hub.

What does the wheel hub connect to?

The wheel hub primarily connects the wheel to the vehicle's braking, suspension, and axle-related components. The wheel and, typically, the brake rotor or drum are mounted to the hub. The hub is supported by the wheel bearing, allowing it to rotate relative to the steering knuckle, axle, or other supporting components. On driven wheels, the hub also connects to the half shaft through splines to transfer driving torque to the wheel.

How does a wheel hub look?

A wheel hub is typically a round, disc-shaped metal component with a central section, located at the center of the wheel. It usually features a hub flange for mounting the wheel and brake rotor or drum, with wheel studs or wheel bolt holes arranged around the flange. The center may include a bearing mounting surface or bore and, on driven wheels, splines for connecting to the half shaft. Modern wheel hub assemblies are typically thicker and more complex because they may also incorporate the wheel bearing, an ABS wheel speed sensor, or a magnetic encoder.

Is a wheel hub the same as a wheel bearing?

No. The wheel hub and wheel bearing serve different functions. The wheel hub is a structural mounting component that connects the wheel to the vehicle, while the wheel bearing supports the hub and allows the wheel to rotate smoothly. Serviceable bearings may be removed, cleaned, repacked with grease, and adjusted, while bearings integrated into a wheel hub assembly are typically replaced as part of the entire assembly.

Is a wheel hub the same as a rim?

No. The rim is the outer part of the wheel that supports the tire, while the wheel hub is the central mounting component that connects the wheel to the vehicle. The wheel mounts to the hub, and the brake rotor or drum is also typically mounted to the hub. The rim and wheel hub are therefore different components.

Does a wheel hub assembly include a bearing?

Yes. A wheel hub assembly typically includes a wheel bearing as part of a preassembled unit. Depending on the design, the assembly may also include the hub flange, wheel studs or wheel bolt holes, an ABS wheel speed sensor or sensor provision, and a tone ring, reluctor ring, or magnetic encoder. The bearing is typically sealed to help protect it from water, dirt, and road debris.

How to Measure a Brake Rotor: Thickness and Wear

How to Measure a Brake Rotor

Brake rotor wear can’t be accurately assessed by visual inspection, driving feel, or mileage alone. It’s recommended to measure rotor thickness with a micrometer or caliper every 10,000 miles or whenever the brake pads are replaced, then compare the measurement with the manufacturer’s specified minimum thickness. When brake pad thickness drops to around 2 mm, replacement is generally recommended to help maintain safe braking performance.

Key Measurements: Rotor Thickness and Minimum Thickness

To determine whether a brake rotor needs replacement, measure its thickness across the friction surface and compare the readings with the manufacturer’s specified minimum thickness. Also inspect the rotor for cracks, deep scoring, and signs of heat damage.

The minimum thickness is often marked on the rotor hat or another non-friction area, or specified in the vehicle’s service manual. Measure the rotor thickness at multiple points around the friction surface, avoiding any raised outer lip, and compare the lowest reading with the manufacturer’s minimum thickness specification. If the rotor is at or below the specified limit, it should be replaced. Any additional damage should be assessed according to the vehicle manufacturer’s service guidelines.

Tools You’ll Need

A micrometer is recommended for measuring brake rotor thickness, while a digital caliper can be used for preliminary checks. You should also have brake cleaner, a lint-free cloth, and a marker on hand.

How to Measure Brake Rotor Thickness Correctly

01.

Choose the Right Measurement Points

Measure the rotor thickness across the friction surface where the brake pads make contact. Avoid the rotor hat, the raised wear lip at the outer edge, ventilation slots, and drilled holes. Make sure the micrometer’s measuring faces sit securely against the rotor’s friction surfaces.

02.

Take Multiple Measurements and Record the Results

Take measurements at multiple evenly spaced points around the rotor, following the manufacturer’s recommended procedure. Record each reading and compare the lowest measurement with the manufacturer’s specified minimum thickness.

To check for disc thickness variation (DTV), compare the readings from different points around the rotor. Excessive thickness variation may indicate that further inspection or corrective action is needed.

03.

Determine Whether the Rotor Needs Replacement

At or below the specified minimum thickness

Replace the rotor.

Too thin to be machined safely

Do not machine the rotor if doing so would reduce its thickness below the manufacturer’s specified minimum machining thickness. Replace it instead.

Within the specified thickness range

Inspect the rotor for other signs of damage and verify that it meets the manufacturer’s service requirements before deciding whether it can remain in use.

04.

Inspect for Other Signs of Damage

Check for excessive disc thickness variation, lateral runout, deep grooves, cracks, severe corrosion, and heat damage. If necessary, use a dial indicator to measure lateral runout and compare the results with the manufacturer’s specifications.

05.

Replace the Rotors and Bed In the Brakes

Replacing both brake rotors on the same axle as a pair is generally recommended, subject to the vehicle manufacturer’s service requirements. After installing new rotors and brake pads, follow the manufacturer’s recommended bedding-in procedure to help establish proper contact between the friction surfaces.

Can You Check Brake Discs Without Removing Wheel?

You can perform a preliminary inspection of your brake rotors without removing the wheels by using a flashlight and a mirror. Check the rotor surfaces for cracks, deep scoring, and visible signs of damage or excessive wear. Also, watch for warning signs such as unusual noises during braking, brake pedal pulsation, or reduced braking performance. In addition, a brake rotor thickness gauge designed for use without removing the wheel can help you perform a preliminary thickness check.

brake rotor thickness gauge designed for use without removing the wheel

However, a visual inspection and an initial thickness check may not provide a complete assessment of the rotor’s condition. If you notice significant wear or the measured thickness is close to the manufacturer’s specified minimum thickness, remove the wheels for a more thorough inspection when practical. Use a micrometer or an appropriate measuring tool to measure the rotor thickness and compare the results with the manufacturer’s specifications. This will help determine whether the rotors need to be replaced to maintain safe braking performance.

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