The use of Stainless Steel Caliper Pistons has also become fairly common.
Stainless Steel does, as claimed, have a lower coefficient of Heat Transfer than the more common Carbon Steel used in standard rebuilds. The reduced heat transfer does reduce the tendency for brake fluid to overheat.
The problem is that it is only Austenitic Stainless Steel that has improved heat transfer and this material also has a much greater coefficient of expansion. As the brakes heat this expansion will increase the stored energy in the seal and this will tend to increase pad knock off and hence pedal travel.
It would be possible to make the piston slightly smaller in diameter to compensate but this would increase cold clearance and affect seal wear.
Most modern race cars are now using Titanium Brake Caliper Pistons. 6AL4V Titanium is almost three time better in terms of heat transfer than Stainless Steel and its expansion is virtually identical to Carbon Steel (in fact 5-7% less) which is how the seal was originally designed.
It does tend to wear in a 'rubbing' application so it is common to coat Titanium pistons to eliminate this problem.
We have just competed a batch of SC caliper pistons (48mm and 38mm diameter) in a TiC coated 6AL4V Titanium alloy.
They will improve the thermal performance of standard SC calipers in terms of brake fluid overheating heating.
