Measuring Caliper Piston Size
 

Hi All,

When measuring caliper piston size is it the diameter of the piston itself (i.e. the part that actually touches the brake pad) or the diameter of the hole in the caliper (includes the piston seals and base)?

I could be wrong, but since the seal actually helps transmit the pressure from the fluid to the piston, the measurement should be taken for the bore of the caliper. I assume you need the measurement to figure out forces and pressures so I would think this would be the most accurate way no matter what.

I've always measured the piston... I don't think that there is going to be 1mm difference between the piston and the bore but I could be wrong.

MG