· 3 min read
Race pads: fade, thickness, and what the caliper is taking
There's 4 mm of friction material left and the pedal still goes long. Thickness tells you almost nothing about a track braking system.
You pull a wheel at the end of the day and look at the pad: 4 mm left. Reassuring. Except that on the third session the pedal went to the floor and the car stopped slowing down.
Remaining thickness is the most visible and least informative measurement on a braking system used on track.
Three different things we all call "fade"
Friction fade. The pad has exceeded its service temperature range. The binder in the compound breaks down, outgasses, and the coefficient of friction collapses. The pedal stays firm — that's the giveaway — but the car doesn't slow. A street compound like Ferodo DS2500 pushed past 1,000 °F does exactly this.
Hydraulic fade, which is really the fluid boiling. The pedal goes soft and travels. That's a fluid problem, not a pad problem — covered in the brake fluid guide.
Glazing. The friction surface vitrifies, often after a single overheat followed by cooling while stationary with the pedal held. Bite disappears permanently on that patch. You recognise it by the mirror finish on the pad.
All three feel like "the brakes stopped working", and all three are fixed differently.
Service range, not absolute performance
Every compound has a range: below it, no bite; above it, degradation. Typical figures:
- OEM pads: roughly 120–750 °F;
- Ferodo DS2500: 70–1,100 °F, still usable on the road;
- Pagid RS29: 210–1,470 °F, cold for the first few stops;
- Endless ME20, Carbone Lorraine RC6: comparable high ranges.
Race pads on the road are a poor choice, and not only for noise and dust: below 210 °F they barely brake at all. That's the opposite of the gain you were after.
What the caliper takes, and why it matters more than the friction material
This is the part thickness will never tell you.
A pad isn't only a wear item — it's also a thermal barrier between disc and fluid. As it thins, that path gets shorter. A pad at 4 mm passes appreciably more heat into the piston, and therefore into the fluid, than a fresh 15 mm pad.
Put plainly: the more worn the pad, the higher the risk of boiling the fluid, at identical driving. The two wear items are not independent, which is why a driver who runs pads to the last millimetre usually discovers both problems on the same day.
A piston seal that has seen 570 °F doesn't return to its original state either. Caliper leaks at the end of a season are rarely coincidence.
The disc: cracks and the lip
Discs wear in thickness, and the manufacturer specifies a minimum — stamped on the hat. But two other signals come first:
Heat checking. Fine radial cracks on the outer edge of the braking surface are normal on a track disc. They become disqualifying when they reach the outer edge or exceed a few millimetres.
Judder. Vibration through the pedal is rarely a geometrically "warped" disc: far more often it's uneven pad material deposition, caused by sitting still with the pedal held on a glowing disc. Never park brake-on when you come back to the paddock.
What to record, session by session
Thickness alone supports no decision. What does:
- Running time since fitting, in hours — not miles.
- The circuit. Road Atlanta and Silverstone don't impose the same thermal load; long straights into heavy braking zones consume far more than a flowing layout.
- The exact compound, because the temperature range follows entirely from it.
- The last fluid flush, whose due date moves closer as the pad thins.
That's precisely what StemmaPass's wear engine combines. Pads aren't counted by distance: the service life it applies depends on the compound read off your invoice — Endless, Pagid, Ferodo, Carbone Lorraine — and the counter advances by track hour as much as by mileage. That's what makes the percentage mean something rather than being long division on the odometer.