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      07-07-2012, 11:30 AM   #11
Naturally agitated
p0lar's Avatar

Drives: 11 E90 M3, 15 WRX STi, 04 M3
Join Date: May 2012
Location: NoVa

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I just wanted to supply an update about a thread I posted over at Though the specs in parentheses are only correct for the E46 M3, the arithmetic and algebra should be consistent across the board. When contemplating master cylinder changes, the overall brake bias of a car is significantly different than what is usually reported, which is simply that of the front to rear caliper measurements, using a single average line pressure for front and rear, which all know to be patently false. That being said, if one stays within the confines of adjustment on the same car, ceteris paribus, only adjusting calipers, rotors and pads, it's OK to neglect line pressure as it's still a linear formula - it's the differential that matters most, either more or less forward than an OEM configuration.

Here is the direct link to the thread I started there, I'll try to keep it maintained/updated to the best of my ability.

If it's so desired, I can make both the F/R caliper/rotor/pad calculations AND overall including MC piston sizes if those are known for the E92 M3 and post them here.

BTW, not ALL BBK manufacturers post the piston diameters on the caliper, or the piston. I've got on the order of at least a dozen different Brembo calipers in my hands at this very moment, and I can easily count on one of those hands, unfortunately, how many actually cast the size of the piston into the caliper.

Totally off the topic: the best way to make the determination is to remove the pistons from one bank using a small fitting (10mmx1.0mm thread pitch adapted to a tire valve) and a bicycle pump. Using an air hose can be dangerous, not to mention the increased likelihood of damaging a ceramic-topped piston as it ejects from the cylinder bore at a ridiculously-high velocity (which directly translates to kinetic energy). Ask me how I know this, even when I covered the piston in question and took reasonable measures to ensure it wouldn't get damaged. NOW, I have a very specific "device" that covers one piston in its entirety, such that when it does "pop", it is pushed into a 1/2" rubber-foam lined cavity. Then, measure the piston -- SOMETIMES, in caliper/piston combinations that have been in service for quite some time, that they have a slight taper from front to rear. It's interesting to me, though I can't find rhyme or reason as to why that is the case. Either way, I'm always absolutely certain to mate the original pistons to their respective bores, even if I'm certain they're well within sufficient operating tolerance to behave correctly.

Ok, enough about that - I hope that post helps someone!