It is well understood that conditions encountered during racetrack driving are amongst the most severe to which vehicle braking systems can be subjected. High braking pressure is combined with enormous energy input and high temperatures for multiple braking events. Brake fade, degradation of brake pedal feel, and brake lining taper/overall wear are common results of racetrack usage.
This paper focuses on how racetrack and high energy driving-type conditioning affects the performance of the brake caliper - in particular, its ability to maintain an even pressure distribution at all of its interfaces (pad to rotor, piston to pad backing plate, and housing to pad backing plate). Pressure distributions between the brake pad and caliper piston(s), between the caliper housing and pad, and between the pads and rotor with new and post racetrack or fade tested brake linings were measured at low, medium, and high pressure and with green and fade-conditioned linings. for several different caliper designs - aluminum sliding, cast-iron sliding, aluminum fixed, and aluminum ‘reverse-pin’ sliding. In addition, caliper suspension efficiency and caliper piston force efficiency were measured for the aluminum sliding caliper design with new and post fade-tested brake linings. The results were analyzed to see how the different caliper designs respond to high energy conditioning, and to illustrate to what extent the caliper (as opposed to the brake lining) is responsible for degradation in brake corner performance. All brake pad to rotor pressure distribution measurements were static (rotor not spinning), but some piston to pad and housing to pad measurements were made both statically and dynamically.
It was shown that both radial and leading-trailing lining taper wear shifts the center of pressure on the outboard housing significantly away from the bridge in the ‘Fist’-style sliding caliper designs, whereas the reverse-pin and fixed calipers maintained a more even pressure distribution. It was also shown that the Fist-style sliding calipers experience higher piston load offset from center than the reverse-pin or fixed calipers, which can reduce clamping efficiency. Suspension efficiency measurements on a Fist-style caliper indicate that force losses through the suspension can be high enough to affect caliper efficiency, and also give evidence that caliper bracket deflection can play a role. Pad to Rotor pressure distribution measurements indicated that the effective radii of the brake corner, and their stability versus brake pressure, change considerably during racetrack usage. Housing to outboard pad measurements on the Fist-style calipers revealed that the distance between the centers of force on the housing fingers and the caliper bridge increases markedly with post-fade tested linings, which can greatly increase fluid displacement for a given pressure. These results were reflected in high performance dyno testing on each brake corner.