Disc brakes stop car wheels using pads that push against thick metal rotors to stop a vehicle. The friction created by brakes generates great amounts of heat, which uses up both pads and rotors; a lot of braking energy is lost as heat.
Since pads are an expendable part and designed to wear first (and actually wear out), pads are a sacrificial part, and rotors are the expensive part. If you regularly check the remaining thickness of your pads it is much more likely you replace them before you need to replace your rotors.
After you read this article, you will be familiar with the thickness of new pads, when you should replace brake pads, how thin is too thin, and how to measure brake pads.
What Thickness Do Brake Pads Start At?
Every manufacturer will have some thickness variation with respect to new brake pads in different make vehicles. But as a rule of thumb:
- New front pads will be 12mm thick (roughly 1/2″).
- New rear pads can either be the same or perhaps a bit thinner in the range of 8 to 10mm (about 3/8″).
In some cars a new set of front pads may have thickness variation between the inner pads and the outer pads, however when these conditions exist, the wear rate is different between the inner and outer pad as a result of the operational behavior of the brake calipers.
When this behavior is anticipated, the manufacturer attempts to size the pads so both inner and outer will be replaced at the same time.
Minimum Brake Pad Thickness
The minimum pad thickness is about 2-3mm (1/8).
This is an absolute minimum thickness, and indicates pad replacement is required immediately. You should limit your driving and get the car to your favorite brake or repair shop as quickly as possible.
Any extended driving with pads this thin can create excessive wear to the rotors, potentially adding to your repair job’s expenses.
Also, the actual braking performance can be compromised with this pad thickness, causing longer stopping distances and potential collisions.
Recommended Brake Pad Thickness
When looking at pad thickness, you should note if this value was approaching the minimum limit mentioned above. For example, 4mm would be usable but very near to the end of the pad’s useful life. Don’t plan long trips.
The halfway point of front pad life would be around a thickness of size 8mm. If you check your front brake pads and see this thickness, then your pads are halfway to the mileage you’d have to replace them.
If you checked pad thickness, and you were between 6mm to 12mm (front brakes), then you are in the recommended thickness range, where it is likely your brakes will perform well, and you will not be replacing brake pads.
Why Do Some Pads Wear Out Quicker Than Others?
As stated before, driving habits will affect pad wear. Aside from that, pad life will mainly depend on the pad friction material discussed in this article.
To summarize:
- Cheap pads made from organic materials will usually be soft and will wear out faster than other pad types.
- Semi-metallic pads are harder than organics and are made with more durable material. They will have better stopping power and last longer than organic pads.
- Ceramic pads have better heat management than organics or semi-metallics and are made of more durable material. They will usually have the best life.
How to Measure the Thickness of Brake Pads
This measurement can be made without removing the wheels. The only requirement is that the wheels have openings that are large enough to see and access the outer pad ends.
If the wheels do not have large enough openings, or truly no opening, the car will need to be jacked up, and put securely on jack stands or tires, and then removed to evaluate the thickness.
Tools Needed:
- Flashlight or equivalent shop light
- Measuring gauge tool (a metric long-handled hex-key set can work too)
Measuring the Thickness of Brake Pads
- Find any accessible end of the brake pad on either side of the brake caliper.
- Hold the flashlight so you can light up the area you wish to measure.
- Place the measuring tool (or hex key end) at the exposed pad end and in contact with the rotor surface.
- The correct thickness tool will fit snuggly in between the rotor surface and the backing plate of the pad. You may try quite a few tool sizes to find the one that fits best in the space.
- Read the thickness value stamped on the measuring tool. That will be the pad thickness.
Can Pad Thickness Be Measured Without Removing the Wheel?
Usually, the outer pad thicknesses can be measured with the wheels on the car. Just knowing the outer pad thicknesses will tell you whether the pads either have wear left or need to be replaced.
An outer pad thickness of less than 5 mm thin is a great indicator that the inner pads should be checked too. If there are any questions about pad thicknesses, take your car to a qualified service technician instead.
When it is time to change your brake pads and you have experience with DIY repairs, you might find the following articles on this site helpful:
Are All Brake Pads Created Equal?
First, your driving style will drastically affect how long your brake pads and rotors will last. However, brake pads are not all created equal.
Notice that brake pads contain two components: The steel backing plate (which is what the caliper pistons push against), and the friction material part (or parts) that rub against the brake rotor. Additionally, those two components are the same for all brake pads.
So then, what differences lie between brake pads?
First is the bonding of the pad’s friction material and steel backing plate.
Some pads use soft metal rivets to secure the friction material. Others use a high temperature adhesive to bond the friction material to the backing plate.
Either way, the remaining thickness limit will be approximately the same. Pad replacement must be done before these attachment means (whether rivets or adhesive) hit the rotor.
Second, and the bigger difference between brake pads, is the friction material used in the friction segments. A wide range of materials are used, and will each provide different brake life and performance.
How often should I Check my brake pads?
About every 5,000 miles. This would coincide nicely with an oil and filter change.