What is brake fade, and why does it happen on track?

Pad fade

The pad has passed the top of its operating window. Its resins break down and gas or a glazed layer forms at the interface, so μ drops. The pedal stays firm, but the car decelerates less for the same effort. It is typical of street pads used on track.

Fluid fade

The fluid in the caliper boils. Vapour bubbles compress, so the pedal travel increases and the pedal feels soft, sometimes reaching the floor. It happens when the caliper temperature exceeds the fluid’s (wet) boiling point, which is why old fluid on a hot day is a dangerous combination. Pumping the pedal may temporarily recover it. It is the more dangerous of the two, because it can arrive suddenly.

Green fade

New pads release volatile resins the first time they get really hot. Until that has happened under control — during bedding — they can fade early. Bed new pads before a track session, not during it.

Mechanical fade

At very high temperatures, discs expand and calipers flex, and the system’s geometry changes. It is rarer on modern road cars, but a contributor on heavy cars repeatedly braked from high speed.

How to prevent it

Pads matched to the temperatures you will reach; high-temperature fluid, fresh; bedding done before the session; brake cooling ducts where possible; build heat progressively in the first laps; a cool-down lap without using the brakes hard; and never hold the brake pedal on a stationary car after a hot session (see hot spots).