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      09-29-2020, 03:10 PM   #9
Captain Caveman

Drives: AW 2013 e92 M3
Join Date: Oct 2015
Location: UK

iTrader: (0)

Originally Posted by M3SQRD View Post
To calculate brake torque you also must include the radius of the rotor. The mean diameter of the AP 372 mm rotor is 345 mm whereas the stock 360 mm rotor has a mean diameter of 326 mm - the AP mean radius is ~6% larger than the stock mean radius.
Indeed. I am asking about piston size in isolation of disc diameter for the time being, as it has a direct impact on pedal travel and firmness, as well as the degree of modulation available. Most aftermarket BBKs offer increased disc diameter and larger pad area, for example the equivalent Stoptech kit, yet their kit retains a total piston area only 1% different to stock.

I'm not doubting the AP kit for a second, I'm simply curious as to the reason for the reduced piston area on AP kits, as it's not the first time I've noticed that they tend to go for smaller total piston areas (seen it before on Evo AP kits). There is obviously a reason for this, and being little more than a novice in this area myself, I'm very interested to understand the rationale. I for one hate a mushy pedal, and like the reassurance of a firm one when pressing on, so perhaps this is the reason they've done this?

I'll leave the Essex guys to spread the knowledge.


Last edited by Captain Caveman; 09-29-2020 at 03:23 PM..