How much brakes for an endurance racer Miata? | Project Endurance Race Miata

Our LFX Miata’s first test day had ended in failure–brake failure, to be exact. Now it was time to fix them.

Our goal? Consistent brakes throughout the 2-hour stints we hoped to run in endurance racing. Let’s get started.

 

First Stop: Define the Problem

Before we changed any parts, we needed to define our problem.

“The car’s brakes are bad” is way too broad of a statement to start planning improvements.

Upgrading brakes after saying that would be like changing the starter if your car doesn’t start. Sure, the brakes could be the problem, but there are also many other reasons the engine isn’t firing.

So let’s diagnose our Miata. We’ve written articles taking a deeper dive into each of these subjects, so for this we’ll just point back to the basics: The brake’s job is to convert the energy of the moving car into heat. Period.

Things the brakes don’t do? They don’t grab the pavement–that’s tires. They don’t dissipate that heat–that’s physics.

All the brakes do is turn the energy of spinning wheels into heat. We find it’s easier to think of this problem as a big interconnected system, just like the car itself. Energy goes into the system via the speeding car, and energy leaves the system via heat.

Our job was to balance this system and make sure the wear items involved in the process would last a whole race. Do both of these at once, and we’d solve our braking problem.

So here’s the problem restated: After multiple back-to-back laps at speed, pushing our Miata’s brake pedal didn’t result in the car slowing. After letting the car cool down, the brakes worked as expected. Inspection back at the shop showed noticeable brake pad wear after one test session.

With the problem written out, it was obvious we had two issues to focus on: Increasing the system’s capacity to deal with the energy going in, and increasing the lifespan of the parts involved.  

Let’s start with the heat problem: We couldn’t change the amount of energy going into the brakes without driving slower or adding tons of drag (damn physics always ruins the fun). So we needed to find a way for the system to better manage that energy.

There are three ways to better manage heat energy in brakes: Use materials (pads and fluids) that operate at higher temperatures without issue; increase the thermal capacity of the system so energy has less of an effect on it; or increase the rate of energy transfer so heat leaves the system faster.

Sound complicated? Here’s an easier way to think about it: Right now, our Miata was the automotive equivalent of a frog in boiling water. We can’t turn the stove off, but there are other solutions: Build the frog out of temperature-resistant materials, increase the amount of water so it takes longer to boil, or point a fan at the pot to blow some heat out of it.

What’s all this mean in practice? We were already running high-temp pads and fluid, so now we’d be adding brake ducts to our race car, increasing the size of our front brake rotors, and adding more front brake pad material. Let’s make it happen.

 

Stop Two: Bigger Brakes

We know: We just wrote 500 words about how bigger brakes aren’t always the answer, only to write “So anyway, here are the bigger brakes.” Hey, sometimes it really is the starter that needs to be replaced….

We loved the lightness of our Wilwood Forged Dynalite Big Brake Kit but wanted bigger, thicker brake pads.

Our reasoning was simple: We didn’t feel that we’d be able to get 8 track hours out of one set of pads, which would cost us valuable time in the pits.

The solution? Bigger calipers with bigger, thicker pads.

So we called V8 Roadsters and ordered its NA/NB Miata Wilwood Big Brake Kit.

For $1044.99, we’d trade our 11-inch rotors for 11.75-inch pieces, and we’d essentially move up a level in the Wilwood caliper hierarchy to parts with thicker, bigger pads.

Installation was plug-and-play, and everything bolted together with V8 Roadsters-provided caliper brackets and rotor hats. We even reused the braided lines from our previous setup.

Total weight gained? After breaking out the scale, we were pleasantly surprised to see this change added only 1 pound, 11 ounces, to each front corner of the car, with only 4 ounces being rotating mass.

For a total weight gain of less than 4 pounds, we’d significantly increase the size of our brakes.

Just to be safe, we also replaced our Miata’s master cylinder with an identical OE replacement while we had the system open. We consider this preventative maintenance whenever a race car has been sitting.

Brakes upgraded, we figured we’d added energy capacity in two ways: These parts should be able to absorb slightly more heat before overheating due to the increased thermal mass, and we’d now have more brake pad material on hand to last a full race. We were making progress.

 

Stop Three: Brake Ducts

But we didn’t think bigger brakes alone would solve our problem: We wanted to drastically increase the amount of heat leaving the system, and so far, our only change in that department was a bit more surface area on the parts. Yeah, that wasn’t going to cut it.

Fortunately, we’re not the first people to build a high-horsepower Miata, and the folks at Good-Win Racing were happy to share what they learned with their own LFX-swapped track car. Their answer? Three-inch brake ducts from Singulär Motorsports.

At $309, its kit includes inlets, hose, clamps and custom-made backing plates to aim the ducts at the center of each front brake rotor. We drilled a few holes in our air dam (more to come soon on that part), then bolted on the kit.

 

Stop Four: Stop.

We’d thrown parts at our Miata, but had we actually fixed the problem? To find out, we went back to the track for another test day.

And, well, it worked. Instead of losing brakes, this time we had consistent, stable brakes for the entire session. Success! Now to finish the rest of the car.

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