How Hot Do Your Car’s Brakes Get?

In this video we are checking out the rear disc brakes of a Honda S2000 using a Flir T1K thermal camera. I’ve got the rear of the car up on jack stands, and I’ll be turning the car on, placing it in first gear, and running the rear wheels to observe the amount of heat generated by the rear brakes.

We’ve got five data points to observe while the disc is heating up. Point 1 is the leading edge of the brake pad. Point 2 is the brake rotor before the brake pad, point 3 is the brake rotor after passing through the brake caliper, point 4 is the wheel hub, and point 5 is the back of the brake pad.

Eventually I’ll be pulling the hand brake, but to start off you can see that as the brake disc rotates, a portion of it is slightly hotter than the rest. It’s important to note that this camera is extremely sensitive to temperature variations, so even a slightly warped rotor, or a rotor with just slightly varying thickness, will easily show up based on the temperature differential. I can’t feel any vibration form the rotor while driving, but it’s cool that this is something you can visualize with a thermal camera.

Revving up the engine, there are currently no brakes applied. Now I’ll continue to rev the engine, and at this point I am lightly applying the rear parking brake, and temperatures are beginning to slowly rise. It is interesting to see that the point after passing through the brake pad is indeed a bit hotter than the point before entering the brake pad, even though the time duration from point to point is so small.

Revving the engine at about 3000 RPM and simultaneously pulling the handbrake, we can see temperatures as high as 138 degrees. It’s also pretty neat to see the interaction at the very front of the brake pad. It seems that while the surface of the brake pad gets super hot, that heat hasn’t yet passed though the depth of the pad entirely.

Brake rotors and pads in street use typically won’t see temperatures exceeding about 200 degrees Celsius, however on track days where the brakes are continuously burdened, temperatures can exceed 500 degrees, or about a 1000 Fahrenheit, pretty easily. The brake fluid itself can also get hot, which is why DOT 3 & 4 brake fluids are designed to have a boiling point over 200 Celsius. This number will drastically reduce, however, as the brake fluid ages and ingests water. Brake systems are not perfectly air tight, and brake fluid is hygroscopic, meaning that it absorbs moisture from the air. This is why it’s important to change your brake fluid every few years, especially if you track your car, to ensure the fluid never reaches its boiling point and you experience significant brake fade.

You can also see on this vehicle, even after the brake rotors reached temperatures well over 100 Celsius, that the brake line itself is actually quite cool. What’s more critical, however, is that the brake fluid within the caliper and actuating the caliper piston remains below its boiling point.

It’s also interesting to see that it seems wheels can act as a heat sink for your brakes, as the heat from your brakes passes to your wheels, and then to the ambient air as the wheel spins. It would certainly be interesting to see if certain wheel materials, whether steel, aluminum, or carbon fiber, would allow for better braking performance as a result of improved cooling of the rotors.

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