Measuring Rotor Thickness

It's impossible to tell how much life is left on the brake rotors by simply looking at it. As a matter of fact, it's dangerously misleading! By simply looking at brake rotors, most rotors seem to be wearing fine unless there are cracks or huge chunks missing.
However, that is where the huge misconception lies.
Unlike brake pads, which show how much pad is left and have warning sensors, brake rotors have no such indicators. It's important for the safety and performance of your car to inspect these properly. We recommend to inspect your brake rotors every 10,000 miles to make sure they are within specs.
Follow our visual guide on how to inspect your brake rotors in just 6 steps. Make sure your rotors are cool prior to inspecting.
Note: If you observe any one of these 6 symptoms, it's recommended that you replace your brake rotors.

1. Visible Cracks
One of the most obvious ways to check when your rotors need to be replaced is through visible cracks. If you see a crack, it's time to replace your rotor. However, in certain cases small hairline cracks are normal if you race your car, such as track days and timed performance events. Keep in mind if you don't know the difference, it's better to be safe than sorry.

2. Grooves
 If you have an open-spoke wheel design, you can run your finger vertically down the brake rotor friction surface. If you can feel and see noticeable grooves, then it's time for new brake rotors.
For cars with hub caps that don't expose the rotor, you will need to remove your wheel to inspect your brake rotors.

3. Rotor Edge Lip
On worn brake rotors, if you follow the rotor to the edge you can usually feel/see a noticeable lip. This lip is created as the brake pads normally don't contact all of the rotor surface and therefore leaves an outer lip when the rotors are worn down.
Keep in mind that rotors reach their wear limit at only about 1mm. If there is an obvious lip, it's most likely near it's wear limit or is wearing unevenly. Measure with calipers to double check.

4. Heat Spots
Heat spots (Fig. x) are a tell tale sign that your brake rotors have uneven brake pad deposits. How do they affect you? Heat spots  will lead to brake harshness, vibration and reduced structural integrity. Heat spots on brake rotors occur when brakes aren't broken in (bedded) properly and the brake pad deposits on the rotor accumulate and eventually turn into a compound known as cementite. You don't want Cementite on your brake rotors. Cementite is compound that is very hard, overly abrasive and doesn't allow the rotors to cool properly. As a result, Cementite heats up the local area around itself growing in size and reducing the cooling capacity of your brake rotors.
Prevention: Properly breaking/bedding in your new brake rotors is vital to the longevity of the rotor. See our Brake Rotor Bedding Guide.
If this is caught early on, you can possibly remedy it by bedding in your brakes with a more abrasive pad, or resurfacing your rotors. If the heat spots are extensive, you will need to replace your rotors.

5. Rust
There are two types of rust that occur on brake rotors. Surface rust and corrosive rust. Most of the rust on brake rotors is known as "surface rust". Just like it sounds, imagine surface rust on brake rotors as a thin top layer of rust. This doesn't affect braking performance and most of it wipes off when you apply your brakes. Although some of it remains, such as on the hub and rotor vents, it doesn't hinder performance but it can be unsightly.  Our zinc and e-coated rotors aid in preventing such rotor rust from forming and tarnishing your beautiful brake rotors.
Corrosive rust on the other hand is the evil twin brother. This is the rust you see when you live in harsh conditions where road salt (electrolytes) is often used. You don't want this type of rust. This rust often happens when you neglect your car and let it sit for extended periods of time without driving, allowing the rust to etch into your rotors. This affects the structural integrity of your rotors as well as effectiveness. If this happens, we recommend replacing your rotors.
BP Coated Rotors are specifically coated with a zinc coating to protect against surface rust.

6. Warped Rotors
Although the term "warped" rotors is very commonly used, it's in fact one of the least common causes of brake vibration. In fact, what happens in almost every case of a warped rotor is simply uneven pad deposits or heat spots. Uneven pad deposits happen from using incorrect break-in procedures. Follow our break-in guide (also known as "bedding your pads") to prevent vibration and premature rotor and pad failure.
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