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

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Update by Tom Suddard to the Mazda Miata project car
Nov 4, 2022 | Mazda, Miata, brakes, Mazda Miata, Good-Win Racing, V8 Roadsters, Singulär Motorsports

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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Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
11/3/22 12:54 p.m.

What pads did you have in the car previously, and what did you replace them with?

Tom Suddard
Tom Suddard GRM+ Memberand Director of Marketing & Digital Assets
11/3/22 1:14 p.m.

We were running Wilwood BP-30s, but switched to BP-40s with the new brakes due to supply-chain constraints. We're planning a return to BP-30s at Wilwood's recommendation, but are going to test out some other brands, too.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
11/3/22 1:24 p.m.

I run BP-40s on the V8 car. They seem to handle the heat of a V8 car at high altitude reasonably well with 3" ducts. I'm using a typical 11" rotor with the Dynalite 6A calipers. I'll bet the best thing you did were those 3" ducts.

Might be interesting to try a back to back comparison. Looks like the 30 gains friction as temps go up, but the 40 is more consistent at a lower peak friction. How do the 30s feel, say, after a safety car or a pit stop?

Wrighty
Wrighty New Reader
11/3/22 2:56 p.m.

Well for a start you shouldn't be blowing cooling air at one face of the rotor...

Rgvkiwi
Rgvkiwi
11/3/22 4:13 p.m.
Wrighty said:

Well for a start you shouldn't be blowing cooling air at one face of the rotor...

Just logged in to say the same, The Singular brake ducts are excellent but you really do need to blank off half the rotor side to direct all air to the inner vanes and away from the inner rotor surface if you want to prevent the rotor from cupping and cracking on the outer surface.

We had this problem until we blanked off the exit hole and then later fine tuned that with a ramp to flow the air rather than just block it.

Further to the article, the 11.75" rotor with the bigger caliper is an AWESOME brake setup and a massive jump up in performance from the Dynalite 11" setup.

We also later deleted the booster (we changed the master cylinder to compensate) and that was the next level again.

I LOVE my brake setup :)

racerfink
racerfink UberDork
11/3/22 4:26 p.m.

I've never had a problem with the stock brakes with Hawk pads when I ran Spec Miata in Florida.  Labor Day weekends at Sebring can get plenty hot.

I run with some guys in a 96 Miata with a 2.4L Ecotec swap and Wilwood big brake kit in Champcar now.  All the big brake kit did was make the tires easier to lock up.  
 

Wasn't there a thread here that talked about how bigger brakes do nothing for braking distance, but a bigger tire contact patch does help distance?

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
11/3/22 4:28 p.m.

If you just put big brakes on the front and don't do anything about proportioning, you'll increase your stopping distance. But if you adjust the proportioning, you'll be able keep your minimum single stop distance while adding heat capacity for multiple stops. It's really important to separate single stop distance from heat management, as they're two different aspects of braking performance.

codrus (Forum Supporter)
codrus (Forum Supporter) GRM+ Memberand PowerDork
11/3/22 4:47 p.m.
racerfink said:

I've never had a problem with the stock brakes with Hawk pads when I ran Spec Miata in Florida.  Labor Day weekends at Sebring can get plenty hot.

Spec Miatas make, what, about 120 at the wheels?  An LFX should be making at least double that, probably more like 2.5 times.

 

racerfink
racerfink UberDork
11/3/22 5:09 p.m.

In reply to codrus (Forum Supporter) :

The '96 Miata I run in Champcar has a 2.4L Ecotec in it, making nearly 200hp.  At Harris Hill, it hits 100mph in four different places, followed by corners that are at best, 50% of that speed.  With the Wilwood big brake kit, you have to be VERY easy on the brake pedal, otherwise you will flat spot a tire.

My Spec Miata would hit the rev limiter in fifth gear at Daytona in a bump draft.  That's roughly 135mph.  Turn 1 there is about 45-50mph.  The stock rotors (it was a '90, so smaller brakes than the 1.8L cars) with Hawk pads had a much better feel, were less prone to lockup, and felt great all the way through an hour and a half "enduro", and two thirty minute sprints.  The SM minimum weight is over 200lbs heavier than what the Champcar Miata is right now.  The Champcar Miata even has much wider tires, but it is so much harder to threshold brake due to feel.

 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
11/3/22 5:26 p.m.

There are different calipers available from Wilwood, some flex more than others. That's why we don't use the base Wilwood kit, we upgrade the calipers to a higher spec. And the sizing of the pistons has to be right. There are a lot of factors to consider in brake design.

But the first thing I'd do on the Chumpcar would be to install an adjustable proportioning valve where the driver could reach it, and service the rear brakes. Then I'd start looking at pad compounds.

z31maniac
z31maniac MegaDork
11/3/22 6:04 p.m.

In reply to Keith Tanner :

The proportioning valve can't be underestimated. I just had mine under the hood on my NA because it was an HPDE car, but I spent a lot of time dialing it in. Even though I had the 4 wheel Wilwood kit that was properly sized, dialing it in with the valve helped. I also ran the common Carbotech XP10/8 combo. 

One weekend I had an ex-Porsche cup driver as my instructor and she commented that she had never been in a student's car with such great brakes. 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
11/3/22 6:16 p.m.

In reply to z31maniac :

When Car and Driver tested my Locost, the big surprise was how well the brakes worked. 911-levels of braking from four little 195-series tires. Some of that was weight, but a lot of it was properly tuned proportioning. Brakes can't create traction, but they can definitely fail to take advantage of what's there. 

I have the prop valve driver-adjustable in my track Miata, and I'll often spend the first few laps of a track day dialing it in for the conditions. Freaks passengers out a bit but that's their problem :)

clshore
clshore Reader
11/6/22 3:30 p.m.

+1 on brake bias adjustment.

The tires stop the car.

A tire delivers best braking when it is on the threshhold of locking up.
A locked up sliding tire has less less stopping power than a rolling tire.

If either the fronts or rears lock up first, your overall braking has been compromized.
The best braking will occur when all 4 tires are at threshold of locking up.

The fronts do the majority of the stopping due to weight load transfer under braking.
Once you lock the fronts up, you are screwed and cannot stop any faster.

There's a reason that serious racecars use adjustable brake bias setups.

kevlarcorolla
kevlarcorolla Dork
11/6/22 6:49 p.m.

I don't think there's such a thing as too much brake for an endurance car,too much cost for proper brakes sure.

 Our 9th gen civic with stock'ish power levels has 13" rotors front and rear with 6 piston front and 4 piston rears.

 Brakes are awesome to use as hard as you need without worry,last car was a K24 eg hatch with ITR calipers and mini rotors.

 Being gentle we still used 80% of the dtc70 pads per 8hrs while the new car is approx 1 set for 32-36 hrs and actually using them as intended.

 Big upfront cost but does offer real savings in pads alone plus hard to put a dollar value on having confidence in the brakes.

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