Does anyone know the piston diameter of the standard 790 master cylinder and front calipers??
Brembo
M50 30mm Pistons
P4 30/34mm Pistons.
CNC GP4-RX 32mm Pistons
CNC GP4 RR 32/36mm Pistons
M4 34mm Pistons.
M50s recommend a 16mm Master Cylinder,
M4's recommend a 19mm Master Cylinder,
For most people a ratio of volume from the calipers to the master cylinder of 27:1 is good
Different ratio’s change the feel of the brakes so:-
30:1 - soft feel
27:1 - sweet spot for design
23:1 - firm feel
20:1 - wooden feel
So to figure out what the volume of each is, you have to take the piston size, divide it by two, then multiply it twice by 3.1416
So, if we look at with a master cylinder at 16mm 16/2=8
3.1416 x8x8 = 201 sq. mm.
If we had 30mm pistons in the calipers, 3.1416 x15x15= 706.86 sq. mm per piston, 8 piston in a dual disk system = 8x706.86= 5654.86sq mm.
So for a 16mm master cylinder we would get 5654.86/201 = 28.13:1 – which would give you a feel a little on the soft side
If we change the master cylinder to 17mm we would get 5654.86/227 = 24.9 firm
If we change the master cylinder to 18mm we would get 5654.86/254.5 = 22.2 firm to wooden feel
Most M50 kits come with a 16mm master cylinder, so the end ratio is 28:1 (a little on the soft side) but M50s with the an 18mm MC = 22:1 which should be between firm and wooden but the M50 smaller pistons holds/moves more fluid. So the feel is good