Summary of Equations:
(for ease and consistency try and use meters and kg)
stopping force = weight of car * longitudal coefficient of friction of tires
Stopping Force = pedal force * brake pad coefficient of friction * mechanical force ratio * (1/radius of the tire) * brake rotor effective radius
.....solve for mechanical force ratio
Front Force = weight front + total weight * tire friction * height of CG * (1/wheel base)
Rear Force = weight rear - total weight * tire friction * height of CG * (1/wheel base)
% front = Front Force/Stopping Force
% Rear = Rear Force/Stopping Force
mechanical force ratio front = mechanical force ratio * %front
mechanical force ratio rear = mechanical force ratio * %rear
Take that ratio and divide it by the pedal ratio.
This is the ratio of mastercylinder bore area and caliper piston bore area.
So say a 4:1 then for a 30cm^2 caliper piston you want a 7.5cm^2 MC or ~28mm bore MC.