Originally Posted by GaryS
Oh, number of pistons was the point? Yes, that's true. Number of pistons doesn't matter. It's the total surface area of the pistons that matters, at least for braking force.
In the stock 135i calipers, having three small pistons instead of one or two big ones might actually be causing problems. We've seen evidence of some kind of uneven or incorrect piston pressure when the brakes are stressed, which the RacingBrakes guy said was a big cause of his rotors cracking in my car and FocusedIntention's car.
You can add me to the list as well. Although I'm not entirely positive my rotors cracking was directly attributable to the caliper pistons I have identical cracking on both rotors after tracking car last time out.