How Hot Do Your Brakes Get?

How Hot Do Your Brake Rotors And Pads Get?

Products Used:

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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[WarpedYT]

200°C .... try this same thing on a Chevrolet Cargo Van, they will probably be 400°C, they are very undersized IMO.

[GearsandGasoline]

That was incredibly interesting! Thanks for the insight Jason! Does the reflective surface of the rotor skew the data?

[scott]

As a brake engineer, yes, aluminum wheels improve brake fade performance vs steel wheels (of course shape of wheel plays a role too). I have never tried carbon fiber yet it should be worse since it's thermal conductivity is typically less than Aluminum. Yet that also depends on the carbon fiber and once again wheel shape.

[supramanx]

Wheels certainly Can absorb and transfer heat from the brakes of a vehicle.
When I worked in a shop, this is one way we were sometimes able to spot brake issues with a customer vehicle when doing inspection during routine services like oil changes and tire rotations. While inspecting brakes for pad thickness, adjusting tire pressure or rotating tires, you can sometimes notice that one wheel is significantly hotter than another (sometimes to the point where you can't touch it bare handed!), or spins much less freely than the other. More often than not when this happens, you would find the pads to be much more worn on that corner, either from a warped rotor or sticking caliper.

[jmurphy]

Interesting that this is posted today. During NASCAR practice yesterday, it was noted that due to the heavy cars, 3400+ lbs, small tires and wheels, the brakes generate tremendous heat. The brake rotors and calipers fill nearly all of the space within the small wheel so that most cooling comes from ducting the teams add for cooling.
Due to brake technology, the brake systems don't fail anymore but what does happen is that the heat generated from the system gets transferred to the steel wheel and melts the bead of the tire causing tire failure.

[dangidelta]

that's really cool....can you do one on exhaust system ( tailpipe + muffler + catalytic converter, etc

[ElZamo]

If the wheel can function as a heat sink for the brakes, could the application of thermal paste between the hub and wheel increase breaking performance? And which kind of wheel would be better for this purpose (shape and material wise)? As a car and PC gaming enthusiast I am exited for what we could learn from this.

[revmatchtv]

Pretty interesting that the wheels themselves can act as a heat sink and cool the brakes. I just did a Brembo brake swap on my 240sx and posted a how to on my channel. I've got a thermal gun and it it will be pretty cool to see what temps they reach on a track day:

[samk]

this is why F1's are hard on their brakes during their warmup lap, the heat generated will transfer to the tires, warming them up, it isn't just about the friction on the ground, but the brakes keep them warm as well

[speeddemon]

who thought thermal cam is this useful, you are a real creative engineer Jason .

[BBoyXy]

The type of wheel to influence dissipation would be pretty interesting to see

[ets]

It has been my experience as a parking lot racer (SCCA Solo 2) and as a Pro Rally racer, that wheels do in fact work as a heat sink for brakes (aluminum vs. steel). One thing I was never able to determine was at what temperature do brake pads catch fire. As I recall, toward the end of the 3rd stage at the STPR rally in Pennsylvania, it was a tight twisting road racing down hill, and I would be a little too heavy left foot braking, and would come into the Finish Control with my front brake pads aflame. the full metallic pads and Brembo rotors would still be working fine, and I would finish the event without changing them (the pads), the bonding agent of the pads would be compromised, and would soon crumble apart. Videos easily show Rally Cars blasting through corners with glowing rotors, but as far as I know, I'm the only one that was able to ignite my brake pads. When fellow competitors commented that their brake did not catch fire, I simply asked them to compare our Stage times.

[BradenCarlsonAutos]

There's so many potential things to do with this camera! Never really thought about the fact that brake fluid can get quite hot under certain circumstances before.

[lionzoo]

I'm trying to work out some carbon rotors on my Elise. If they ever become operational, you're more than welcome to come over and get some footage of the carbon rotors in action.

[ebrainz]

You'll see many modern race cars actually warming their tires with the brakes. In fact, it is absolutely the best way to warm up the rubber. The only downside is it wastes fuel, so endurance racers are more likely to continue cornering hard to do the same thing.

[arminrud]

When you brake without a wheel, the little screw holding the brakedisc on the axle has to handle with all the torque. With a wheel fitted on the axle, the force is transmitted by the Wheelnuts/bolts. The tiny screw is just for centering (holes in disc are bigger than wheelbolts) and holding the disc when there is no rim to prevent it from falling of.

[ally_vc]

i heard a while back that a company looking into carbon fibre wheels were concerned about about the heat transfer rate compared to metallic wheels and what it would mean for the cooling of the brakes, as I think it goes without saying, these wheels would likely be on higher performance vehicles and the heat transfer would be a lot more crucial.

[hawkeyestiguy]

Just when I thought this channel couldn't possibly get any cooler! Hahaha.

[BurnersCars]

So, what would it take to start seeing a rise in the temperature of the brake fluid? (fascinating video, btw)

[robmeeldijk]

you're having way to much fun with this thermal camera