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      10-01-2020, 05:33 AM   #15
Captain Caveman

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

iTrader: (0)

Originally Posted by jritt@essex View Post
Captain Caveman (great name BTW...I forgot about that guy! ),

As pointed out by others above, it's not just about piston size. To calculate brake torque you have to include the radius at which the clamping force acts upon the disc (known as effective radius). Increasing the effective radius via a larger disc increases the amount of brake torque on a given axle. You also have to take into account brake pad coefficient of friction...
Hi J,@ Essex,

Really appreciate the detailed and considered reply. Again, I am not much more than a novice here, so keen to learn, however I have a logical brain so very curious as to the choices you have made with your kit.

I understand that increasing the distance of the caliper from the centre of the wheel will increase brake torque and hence alter the bias, so you have reduced piston area accordingly to maintain balance. Surely however, this does not compensate for the reduction in pedal travel, and hence increased firmness caused by using a 9% smaller piston area, or is this number simply too little to be significant?

Also - I understand that you might want to reduce piston area on the front as a result of going larger on the disc diameter in order to maintain brake torque close to stock, however as you have actually gone for a smaller than stock disc on the rear, as well as smaller piston area, isn't that counter intuitive?

Obviously I don't want you to give away any proprietary secrets, however can I assume that you have deliberately decided to increase pedal firmness and reduce travel a little, for what you feel is a benefit to pedal feel? Did you perhaps find the stock pedal a little soft or the travel a little longer than optimal? Curious as to the thinking here.