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 …
What pads did you have in the car previously, and what did you replace them with?
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.
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?
Well for a start you shouldn't be blowing cooling air at one face of the rotor...
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 :)
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?
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.
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.
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.
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.
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.
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 :)
+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.
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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