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I did some thermal testing on a new idea I've been working on, and I am amazed (though I shouldn't be) at how little the front brakes cooled between instances of braking. Using a cheap thermometer with dual inputs and a pair of thermocouples, I placed the probes between the brake disc and dust shield (at the top, where there's a little hole in the dust shield where I was able to wire-tie the probe end), with an experimental vent on the left, and stock setup on the right. The brakes are totally stock, and just under 2,000 miles old.






I had my son behind the wheel, and me with the thermometer, doing some datalogging and shooting some (very poor) cell phone video. Even with just a quick 60 - 30 firm brake, then back up to 60, the non-vented side just got hot and stayed there for a while, in addition to getting hotter than the vented side. In an autocross, this would be totally unacceptable. It makes sense, though, why the brakes get so hot so quick and don't cool off. I've noticed brakes are getting bigger and bigger from the factory. It's not just weight, it's aerodynamics! Those aero shields they put all up underneath just don't allow NEW air to get into the wheel wells! The only air that can get in is probably coming from what gaps there are in the splash shield and engine bay, which means the air has already been pre-heated by the engine.

A sleek underbelly may make for good highway MPG, but it's got to be really hard on the brakes of any car with extensive underside treatments like that.
 

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We didn't notice any fade issues in Autocross with stock size rotors, as you know any serious brake use in autocross is usually way too much brake use (slow).

We did notice in track events that stock size was not enough thermal capacity and we found significant fade even with pad upgrades and caliper upgrades.

The splash shields are well engineered to do the job (keep effective braking in the rain). I have driven a Miata in the rain with those removed and one good splash means serious loss of brake effectiveness while the pads 'float' on the layer of water.

Thus, for autocross we suggest stock size two-piece rotors and caliper upgrades to drop as much weight as possible in the classes where legal to do so. But if track use in the plans then thermal capacity upgrade is suggested (bigger than stock two-piece rotors). We have all the options starting AT THIS PAGE.

STOCK Brakes and Battery 84.55 pounds


LIGHT Brakes and Battery Just 31.75 pounds! SAVINGS over 52 POUNDS!
More weight saving info in our Home Forum Thread...CLICK HERE.

 

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I did some thermal testing on a new idea I've been working on, and I am amazed (though I shouldn't be) at how little the front brakes cooled between instances of braking.

...

...the non-vented side just got hot and stayed there for a while, in addition to getting hotter than the vented side. In an autocross, this would be totally unacceptable. It makes sense, though, why the brakes get so hot so quick and don't cool off.
My brakes were just fine at autox. I didn't experience any fade.

I notice you didn't include any numbers in your post.
Were the temperatures within the pads heat tolerance and working range?
What is your goal here? Justification for a brake upgrade?
 

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Discussion Starter #4
We didn't notice any fade issues in Autocross with stock size rotors, as you know any serious brake use in autocross is usually way too much brake use (slow).

We did notice in track events that stock size was not enough thermal capacity and we found significant fade even with pad upgrades and caliper upgrades.

The splash shields are well engineered to do the job (keep effective braking in the rain). I have driven a Miata in the rain with those removed and one good splash means serious loss of brake effectiveness while the pads 'float' on the layer of water.
In my old racecar (the Neon), I ran Power Slot slotted rotors, and they performed very well, even in the rain. Since then, I've been a fan of slotted (but not drilled) rotors, and I run them on all our cars, except the Fiat (so far...?).
With the MX-5, have you had a chance to test any same-size solid-face, slotted, and drilled rotors in auto-X and noticed any advantage/disadvantage to a particular version?

Thus, for autocross we suggest stock size two-piece rotors and caliper upgrades to drop as much weight as possible in the classes where legal to do so. But if track use in the plans then thermal capacity upgrade is suggested (bigger than stock two-piece rotors). We have all the options starting AT THIS PAGE.
Your lightweight calipers front and rear are very near the top of my shopping list! This experiment with the vent kit was to prove/disprove whether or not I'd want to go BIGGER with calipers and rotors, or stay stock size and go for the weight reduction.
I'd say the experiment was a success. That means the lightweight brakes from Good-Win, decide on the coilovers, get final measurements, and then get some 15x10 wheels and slicks :D


I didn't have very high temp probes, so I couldn't measure caliper temps directly, and I didn't do anything really extreme, since we were on public roadways. So I don't have much in the way of numbers, except for some raw video I shot while datalogging. What I ahve so far, with the probe mounted between the rotor and dust shield (basically measuring the heat radiating off the rotor)
Driving 60mph, and firm braking to 30, there was a 10*F difference between vented and non-vented. Not only that, but the non-vented side stayed +5 for more than a minute, so even when not braking, there just wasn't much airflow for recovery. To simulate gonig down a long hill, I had my driver ride the brakes at 35mph, and the difference quickly shot to 25*F in a matter of seconds. Recovery again was much better on the vented side. I know I've seen cars with vents built into the front of the wheel well splash shield (mostly high-end) and the idea actually came from my old race car. When Chrysler engineers developed the Neon ACR, they intentionally included the fascia with fog light holes, but no fog lights, making brake venting very easily added.

As soon as I've cleaned it up and finished the other side, I'll post up this new mod on the Project Mamba build page in the Builds forum.
 

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I have the Brembos and do some pretty aggressive street driving, but no track days, and I have not seen any signs of brake fade. The Abarths in Europe come with DOT 4 brake fluid probably because the Brembo upgrade in Europe is part of the Abarth package. U.S. Abarth's in the U.S. market have DOT 3 like the other models.
I don't know if in the U.S. they upgrade the brake fluid to DOT 4 with the Brembo option or not. I will ask my dealer. But IMO, all these cars should have DOT 4 as boiled brake fluid can certainly be a cause of brake fade.
I will ask the experts though, I think if the brake fade was caused by fluid being heated beyond its spec, cooling the brakes would not get things back to normal since the boiling changes the fluid characteristics permanently and can introduce air?
 
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