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.
I checked back with FocusedIntention not too long ago regarding how he was finding the RacingBrake kit with the caliper rebuild kit, specifically asking him if there was any cracking of the rotors - he said no problems whatsoever with the new batch. Previously yes, but he seems confident that this new batch is up to the task. Wonder what the difference is?