[Bimma360]

Since all of my posts and threads got deleted, and the previous version of this thread got a little spicy, I am going to go about this a little bit differently.

Please Read - This thread is not a place to discuss the merits of a particular upgrade. The purpose of this thread is to quantitatively evaluate how a particular (DIY or off the shelf) BBK's change the factory brake bias, and in some cases explore what can be done to restore the brake bias to factory spec.

The following are the calculations I came up with for various DIY and off the shelf options to see how they relate to the factory brake bias. (This car is still young so I am sure the list will grow a little bit over time).

**Take note, that these bias %'s are not meant to be real world accurate, but instead a comparison to the calculated factory bias as certain variables are changed (rotor size and caliper piston size). In other words, the goal is to see how and to what extent certain rotor and caliper changes deviate from the calculated factory number.

This is the calculator used:

https://brakepower.com/brake-bias-static.htm

A note about "Effective Radius of Brake Rotors," which can cause some confusion:

"The effective radius of a brake rotor is measured from center of brake pad to center of brake rotor. In other words, it is the distance from rotor-center to halfway the swept area of the rotor.

More accurately but less easy to measure: it's the distance from rotor-center-line to center line of caliper piston(s)."


On the the numbers...




*I will update this post/table as we add to it.

[Bimma360]

F95 X5M 6 Piston Calipers w/ Factory Brackets (direct bolt on)

These calipers (also found on a few other models) are a 5 % reduction in total piston area. A reduction in total piston area will reduce brake pedal travel. In other words, one should feel the brakes bite further up in the pedal. Using this caliper results in a 2.4% reduction in front brake bias. What this means is that the car becomes more braking rear biased when compared to stock.

The table shows another scenario where brake pads with differing CoF (0.42 front and 0.38 rear) are used in an attempt to compensate. This, however, increases the front bias from stock by 2.3%.

I know the Brembo GT kit for this car uses a 412mm rotor. Turns out, if you use a hypothetical 412mm front rotor with these calipers it will restore the brake bias perfectly to factory spec. Obviously, custom brackets will be needed. But this would be the optimum set up. Plus all of the advantages of running a larger rotor.

Something to think about: The 2.4% reduction in front brake bias, may or may not be negligible. However, it does take a rotor that is 2/3's of an inch larger in diameter to compensate for running the smaller piston caliper.



Currently, the value I am using for the rear caliper piston diameter is a guess based on what is being used on other models. A different value, can change things. If anyone knows, or is doing a rear brake job and can confirm that would be awesome.

[Bimma360]

Reserved for future Brembo GT 8 piston post.