Designing the front to rear piston areas appears to have not been addressed with this topic. The Silvermine rear kit with 43mm piston gets close to the right front to rear piston area ratio but could be better (I have the 2 piston 43mm/34mm front caliper). Check the graph from this link: http://stoptech.com/technical-support/technical-white-papers/white-paper---brake-bias-and-performance-why-brake-balance-matters . The car for this link has very similar front to rear weight balance as a Z-car statically. Dynamically, though, with race car spring rates, a 30% contribution by rear brake piston area is near the maximum needed. Street cars won't need near as much rear brake. There are other variables such as rotor size, pad material, spring rate, proportion valve that effect brake bias sizing but front/rear piston sizing is the most important. Because of this, I picked a 3 square inch rear piston to balance out the front brakes.