When I bought slotted rotors, autocross brake pads, and stainless steel lines I wanted to make sure the upgraded braking performance wasn’t going to outmatch my regular old brake fluid. As I was looking at brake fluids I realized that I had no way to decide what boiling point was appropriate for autocross. Did I need 660F brake fluid now that I had super grabby brake pads? Would they really generate that much more heat? A brief hop around the forums didn’t reveal much convincing evidence, so I decided to apply some science. I bought the “best value” brake fluid I could find and some temperature labels, and I hit the track in the middle of the summer.
Back in June I covered the basics of brake fluid and listed common, off-the-shelf brake fluids with the published boiling points and some prices. I determined that the Napa brand DOT4 brake fluid would be my testing fluid because it had the best boiling point to cost ratio. With a 480F dry boiling point, it is well above the minimum SAE rating for DOT4 brake fluid. I also knew that I would be using a few liters of brake fluid to flush the system when I rebuilt the calipers and later installed stainless steel lines, so getting a gallon of brake fluid in one swipe was advantageous. Conveniently, I was able to find temperature labels from McMaster-Carr with the same max temperature as the boiling point of the fluid, so I would know how close I was getting to boiling. If I went over the temperature reading wouldn’t be helpful at that point anyways.
The first test of my setup came at the Ultimate Street Car Association Charlotte event on July 30th. It was a broiling day, and the event featured a much more strenuous schedule than the typical autocross. Not only did I manage to accumulate 7 autocross runs, I also made 5 speed stop attempts. This amounted to one heck of a test for the brake fluid, but they never faded. I didn’t have my temperature labels attached to the rotors at the time. At the next CCR-SCCA autocross, I did attach the labels and the temperature of the calipers didn’t even register! The front and rear calipers never reached the 370F minimum of the temperature labels.
Although I was surprised to see that the calipers never even reached the minimum of the temperature labels it was not unbelievable. Autocross requires heavy braking in short bursts to navigate the tight cone courses. These actions are brief and separated by plenty of throttle time. This gives the brakes time to cool off between brake applications. Road course and even circle track racers spend much more time on the brakes, which is why we see carefully planned brake ducting in addition to high temperature fluids and specially designed rotors and pads. For my setup, and likely most in autocross, these things simply aren’t necessary.
What is necessary are some caveats. Braking is the conversion of kinetic energy into thermal energy by way of friction. Many things could increase the rate of heat generation or total heat generated when braking in a different vehicle. For example, I simply upgraded the brake pads and rotors alone. This conversation may be different had I also replaced the stock brake calipers with aftermarket calipers. More braking power means an increase in the rate of heat generation. If the rate of heat dissipation from the rotor or calipers isn’t increased, then they will get hotter. My car is also fairly light with a factory curb weight around 3100lbs. A beefier racecar with big brakes may see elevated temperatures that warrant better brake fluid than the store brand. Since kinetic energy is directly related to mass, a heavier car will put more heat into the brakes in order to brake at the same rate as a lighter car. So, perhaps the title of this article would be more appropriate as, “I Don’t Need $70/L Brake Fluid.” But it’s likely the case that you don’t either. These extreme fluids aren’t only expensive, but they can be tough on your equipment as well. Professional race teams are constantly tearing down and rebuilding their cars, and this includes their brake master cylinders and calipers. The most expensive fluids can cause excessive swell in brake seals, so be sure that you’re on top of your equipment if you’re going to invest in the best brake fluid. Alternatively,there are many options for high temp brake fluids that don’t cost $70/L. If you’re noticing brake fade by the end of your runs, consider ATE TYP 200 brake fluid (536F dry boiling at $13.99/L from BimmerWorld). If you need more than that, StopTech’s STR brake fluid comes in at a competitive 594F dry boiling point at $34/L. These brake fluids also come with the added benefit of greatly increase wet boiling points. If you don’t plan on replacing your fluid regularly (think every 6 months or more), then these may provide a suitable option running a full season on one brake fluid flush because they will still perform when the brake fluid begins absorbing water.
Whatever brake fluid you choose, the most important thing to remember is that your brakes are as much about speed as safety. Always be aware of the state of your brake fluid and flush often. Racing in any form will push the limits of your automotive systems, but if you keep a watchful eye and consistent maintenance schedule then you will always be prepared for racing with confidence.