Project MR2 Turbo: Upgrading the Brakes Via Pads, Rotors & Fluid | Slow Down to Go Faster

Update by J.G. Pasterjak to the Toyota MR2 Turbo project car
Dec 4, 2020

If we’ve said it once, we’ve said it a zillion times: Brakes are the most powerful speed-changing device on your car. Or, at least, they should be. 

So proper braking performance is key to fast lap times, both to correct the speed of the car entering corners and to balance the chassis and give the driver a sense of confidence and predictability over the vehicle.

The brakes on our 1991 Toyota MR2 Turbo did virtually none of this.

We could start with the basic flaw in their design, that being that by all modern standards of brake construction, they are tiny. Heck, even by 1991 standards of braking, they’re not particularly impressive. 

At slightly large than 10 inches in diameter, the rotors are about the size you’d find on contemporary base-model economy cars. For a car delivered from the factory with 200 horsepower and sporting intentions, they were iffy from the factory–and when you add power and speed, the sketchiness just intensifies.

Of course, the solution to little brakes is big brakes, right? Well, yeah, that would certainly solve things. 

Pointing the money hose at stuff is a great way to put out problem fires, but money hoses can be costly to run. Maybe we’ll eventually come to the conclusion that a full brake upgrade is necessary to keep up with the performance of our turbocharged Toyota, but for the moment we’d like to explore the limits of the stock configuration of the brake system. Maybe we can improve the performance without spending huge money or getting into new configuration headaches.

So the first order of business is basic maintenance and replacement of all the consumables with the best stuff we can find. That maintenance begins with a brake fluid test. A $10 brake fluid checker can quickly reveal how much water has gotten into the brake hydraulic fluid, and in our case it was a lot. We should have been tipped off to the fact that the brake fluid was ready for replacement because it looked more like Dr. Pepper than DOT 4, but when the inserted the tester and all the lights lit up and the thing beeped, we had our confirmation. To that point, we didn’t even realize the tester had a beep function.

We sourced all of our brake restoration parts from EBC Brakes, one of the few companies to manufacture both performance pads and rotors for our MR2. 

So, back to the fluid. Their DOT 4 brake fluid has a dry boiling point of 518 degrees Fahrenheit, which was certainly higher than the contaminated, maple syrup-looking concoction currently occupying our hydraulic system. We flushed the system extensively, until we got nothing but clear, clean fluid from all four calipers. Then we flushed a bit more for good measure. 

For hard parts, we chose a set of EBC’s Yellowstuff pads along with a set of EBC’s cryo-treated performance rotors. We keep repeating that the brakes in this car are small compared to what we’re used to, and never is that more apparent than when you’re looking at the pads. A pair of pads fit easily in one hand, and they’re asked to turn the kinetic energy required to power your entire house for a few minutes into heat as you slow the car from a fourth-gear straight to a third-gear corner.

Of course, that energy transfer is created through the friction of the pads on the rotors, but there’s just not a ton of surface area for that friction to be created. So the Yellowstuff pads and cryo-treated rotors make up for their lack of size by having a very high coefficient of friction, grabbing each other with surfaces that produce a lot of heat, very quickly, to slow the car.

As well, that heat has to go somewhere, and tiny pads and 10-inch rotors simply don’t have the mass to be super-efficient heat sinks the way large, modern brakes do. The reality is they’re dealing with as much heat as a set of massive brakes but using a fraction of the surface area and mass to dissipate it. So they’re going to get hot and stay hot. That’s just how it is.

That’s where the cryo-treated rotos come in. By putting the rotors in a super-deep freeze and allowing them to return to ambient temperature in a very controlled temperature rise, the granular structure of the metal in the rotors is further aligned by the controlled contraction and expansion from the temperature extremes. It’s a process similar to work hardening, but without the associated surface wear.

While the cryo treatment doesn’t necessarily produce a rotor with better performance on a given brake application, it absolutely does produce a rotor that is far better equipped to deal with the types of extreme temperatures these rotors will see, dramatically increasing their service life.

Remember the thing we said about the brakes being the most powerful speed changing device on your car? Well, our old brakes barely got the message.

After even a short session on our test track at the Florida International Rally and Motorsports Park, our original brakes were fading, stinking and producing unpredictable and uneven deceleration with each application. We could barely even get into the ABS in some deceleration situations, meaning we were nowhere close to threshold braking. 

Post-installation of the EBC components and fresh fluid, however, things changed dramatically. Of course, it’s not a surprising statement to say, “We replaced our crappy brakes with better brakes and things improved,” but what was particularly dramatic was how the EBC components allowed us to use the brakes more as an attitude-adjustment tool than simply a speed-mitigation tool. That’s a product of good feel and great release characteristics.

It wasn’t just our trained toe telling us things were better. The data showed better braking performance, too. This was nowhere more dramatically seen than entering the particular corner shown in the data: We can see the blue speed trace of the old brakes gently rolling in to max deceleration, while the red trace of the EBC brakes immediately goes to max decel–which is also a much greater rate than the old brakes–and stays there. Looking at the g-cloud on the top, you can also see far more instances of much higher levels of braking, signified by additional red dots below the groups of blue dots.

If it takes less time to slow down, that’s more time you get to spend on the throttle, and our traces show that the EBC-equipped car got back to the throttle much quicker than before. Less time on the brakes and more time on the gas resulted in more than an eight-tenths of a second lap time improvement and, just as importantly, greater ease with which those improved lap times could be repeated.

Cost for the whole setup is less than $1000. The cryo treated front rotors retail for $229 for the set, while the rears fetch $437 retail for the pair. Front pads cost $125, while rears list at $97. That’s not as inexpensive as contemporary Miata or Honda bits, but the relative rarity of the MR2 means that costs on some hard parts can be a bit more precious.

So, braking performance is dramatically improved, and we intend to improve–or at least bulletproof–it further with the installation of some braided lines and a refurbishment of the calipers at some point. 

But ultimately these are never going to be anything more than 10-inch-diameter brakes, meaning that they will always have a challenge dealing with their thermal load, especially now that they can produce so much friction. For a car that mostly sees autocross use, this shouldn’t even be an issue. But track drives will need to be cognizant of their brakes at all times at speed on a circuit. 

Some of this heat load can be addressed with mitigation issues. Good airflow in and especially out of the brake area is paramount, and frequent monitoring of the condition of the brake fluid is also important. Brake fluid subjected to frequent extreme heat cycling is more likely to pick up condensate-based moisture more quickly than gently used fluid.

So we’ll look at more fine tuning of the brake system going forward, and maybe even look toward a full retrofit of large calipers and rotors at some point should we take things in a more track-oriented direction. But for now, we’ve made dramatic, impactful improvements with a very moderate time and budget investment.

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