Last updated September 14, 2021
Disc brake systems for cars and trucks use friction elements called brake pads. Every time you stop, the significant energy from your car's motion is effectively dissipated into heat by the brakes on each of the wheels.
In normal driving, this process is repeated again and again. Although the caliper parts get quite hot, the friction material on the pad and disc gets very hot.
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The energy dissipated at each stop gradually wears down the material of the brake pads and brake discs. In general, a well-designed braking system will wear out the friction material in the pads long before the more expensive rotors wear out and need to be replaced.
The measure of brake pad wear is simply the measure of the remaining thickness of the friction material after a few kilometers have been ridden. In this article we will discuss how to assess pad thickness and what thickness limits require pad replacement.
Are all brake pads the same?
First of all, it should be noted that your driving habits will have a major impact on yoursservice life of your brake padsand rotors. That being said, not all brake pads are created equal.
Remember that brake pads are made up of two components: the metal backing plate (against which the caliper pistons press) and the attached segment(s) of friction material that abuts the rotor. These two components are common to all brake pads.
So what are the differences between different brake pads?
The first concerns the way the friction material and steel backing plate are attached to one another. On some pads, the friction material is held in place by soft metal rivets. With other pads, the friction material is held in place by a high-temperature adhesive.
In both cases, the worn thickness limit is approximately the same. The insert must be replaced before these safety devices (rivets or adhesives) come into contact with the impeller.
The second and most important difference between brake pads is the material of the friction rings. TOvariety of such materialsused, and each type produces a different braking performance and lifespan.
Related:The 5 best brake pads for cars, trucks and SUVs
How often should you check your brake pads?
Pad thickness should be checked every 5000 miles. A good time to do this would be during or after an oil and filter change.
How thick do brake pads start out?
There are some differences in thickness between different makes of vehicle when it comes to new brake pads. But in general this rule can be applied:
- new front padsit will be 12 mm thick (about 1/2″).
- new rear padsit could be the same or slightly thinner in the 8-10mm (approx. 3/8″) range.
On some vehicles, there may be a difference in thickness between the inner and outer brake pads with a new set of front brake pads. On these vehicles, the rate of wear varies between internal and external wear due to the performance of the calipers.
When this behavior is expected, the manufacturer attempts to size the pads so that the inner and outer pads must be replaced at the same time.
Minimum thickness of the brake lining
The minimum thickness of the pad is approx. 2-3 mm (approx. 1/8″).
This is a bare minimum and indicates the need for immediate pad replacement. You must limit your driving and get your car to your favorite workshop or brake shop as soon as possible.
Any lengthy ride with such thick pads can cause serious wear on the brake discs and add extra cost to your braking work. In addition, the actual performance of the brakes can be affected, resulting in longer stopping distances and a higher risk of collision.
Related:5 symptoms of worn brake pads
Recommended brake pad thickness
When checking the pad thickness, pay attention to whether the value is close to the minimum limit mentioned above. For example, 4mm thick pads are usable but near the end of their useful life. Don't plan long trips.
The average lifespan of the front pad is about 8mm thick. If you check your front brake pads and find that they are thick, your pads are halfway to the miles when they need to be replaced.
If you checked the thickness of the pad and it was in the range of6mm bis 12mm(Front brakes) This is a recommended thickness range where your brakes will work well and you won't need a pad change for the foreseeable future.
Why do some pads wear out faster than others?
As mentioned above, driving habits affect the life of your brake pads. Regardless, the life of the brake pad mainly depends on the friction material of the brake pad as explainedIn this article.
Let's summarize for simplicity:
- cheap pillows offorganic materialThey are generally soft and wear out faster than other types of pads.
- semi-metallicThe pads are harder than organic pads and made of a more durable material. They offer superior braking performance and last longer than organic pads.
- ceramicsThe pads tend to manage heat better than organic or semi-metallic pads and are also made from a more durable material. These generally offer the best durability.
How to measure the thickness of brake pads
This measurement can be carried out without dismantling the wheels. The only caveat here is that the wheels should have large enough openings that you can see and access the outside edges of the pads.
If the wheel openings are very small or non-existent, this assessment requires the car to be jacked up and placed securely on jack stands and the wheels removed.
- flashlightor equivalent shop light
- gauge(a metricLong handle hex wrench setcan also work)
Measure the pad thickness
- Locate an accessible end of the pad on each side of the caliper.
- Hold the flashlight to illuminate the area you want to measure.
- Place the measuring tool (or allen wrench) on the end of the exposed pad and against the surface of the rotor.
- The tool of the right thickness fits snugly between the rotor face and the metal backplate. You may need to experiment with different tool sizes to find the best fit for that space.
- Note the thickness value stamped on the measuring tool. This will be the thickness of the pad.
Can you measure the thickness of the pad without removing the wheel?
In most cases only the outer pad thicknesses can be measured with the wheels of the car. If you know how thick the outer pad is, you know the pads are still worn out or need to be replaced.
A very thin outer pad thickness (5mm or less) would be an excellent indication that the inner pads should also be checked. If you are in doubt about the thickness of the pads, take your car to a qualified technician.
If it's time to replace your brake pads and you're a seasoned DIY enthusiast, the following articles on this site may be useful:
- Change brake pads (step by step)
- Rejuvenation vs. disc change
- recent posts
Ron has a degree in mechanical engineering. He has been a car enthusiast for over 60 years. Notable cars in his garage include rotary and turbocharged Corvairs, Alfa Romeos, Corvettes and Mazdas. He brings that wealth of experience to this site to help you successfully maintain and improve your favorite vehicle.
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