If my brakes overheat, do they need to be replaced?

Question

Let's say I take my car track racing, and during it, the hard braking leads my brakes to massively losing stopping power due to them overheating (a likely outcome on stock brakes). Or likewise, I take my car down a gigantic hill and don't use engine braking.

Two questions:

1. Can I let them cool down, then safely drive off to go home?
2. Will I need to replace them immediately afterwards, or just when they get thin as usual?

I suppose the core of this question is "After overheating, do brakes cool down to their original state, or do they substantially lose effectiveness?".

Answer 1

For the majority of brakes, they should be fine after a track day, but the real risks come from significantly overheating the brake fluid, or from stopping with hot brakes and having them cool while parked.

This is why at track days it is always recommended that you stop after ten or so laps, if you have standard brake systems, to allow your brake fluid and brakes to cool.

While stopped, you don't use your handbrake. Instead, use chocks or stones to hold the car stationary - having the handbrake on holds the brake disc during cooling, and this can easily cause warping.

As long as you follow this guidance you should be fine. Obviously, a track hammers your brakes far worse than general driving, so you do run the risk of wearing your pads down to an unsafe level, so get them checked before driving home.

I also find that my tyres only last one track day, so I need to replace them all before heading home - so I tend to only go to track days with a tyre provider on site.

Answer 2

My experience, limited to a few very specific configurations is:

• I've never had rotor warping issues even after a LOT of heat in the brakes (both from track days and also stuck brakes while driving on the express way). I've used generic NAPA rotors, OEM rotors, and fancy heat/cryo treated ones. I can't tell any difference between any of them. They all function like big slabs of metal heatsink. :-)

• The brake pads themselves (including dirt cheap ones, Carbotechs, and Porterfields) have always worked the same after being very hot as before. However, the cheap ones and the Carbotechs (Panthers, a fine brake pad overall, but just not up to stopping a car as heavy as mine with such small brakes and so much power) went in the trash the day after the events I used them as they performed so poorly while hot.

• If you boil the brake fluid, you should bleed the system as it does seem to lose a little effectiveness (but was nowhere near as bad as I had expected). Wet boiling point seems to be more important than dry. I've boiled 2 week old Motul 600, but the off the shelf at the auto store synthetic (with much lower dry boiling point, but higher wet boiling point) is fine in my cars on the track for years.

• A bigger concern is the condition of the caliper seals. I've melted the seals out of the caliper without hurting the pads, rotors, or boiling the fluid before... That happened only with cheap pads, better quality pads have backing plates that provide at least some insulation value. :-)

Answer 3

All of the other answers are great, but I just want to add that rotors are very, very hard to "warp" from 'normal' use (including track day abuse). Any variance in thickness is because pad material has transferred from the pad to the rotor. Turning the rotor gets rid of this.

See "Warped Brake Disc And Other Myths".

Answer 4

In absolutely no expert on the subject of physical properties of metal. However, in relation to this specific question my main concerns would be:

• Will the overheated discs warp during cool-down? This will lead to varying degrees of shaking during braking afterwards (and a replacement.)
• The brake fluid on the other hand should probably be flushed and replaced due to the extreme temperatures.

I wouldn't expect the pads to lose effectiveness¹.

EDIT:

¹⁾ Other resources suggest that pads can be glazed.