40mm Rear Caliper Viper Brake Balance
What do "larger" rear brakes really do? They increase the clamping force on the rotor such that the rear tires do more work to provide vehicle deceleration. However, with too much clamping force the rear tires may lock up and the car will lose directional control.
As a safety measure, all vehicles come from the manufacturer with fixed rate proportioning valves installed. Installing aftermarket four-piston rear brake calipers greatly increase the rear braking capacity but will exceed the capability of the factory proportioning valve. 1992-2000 model year Vipers will need to add an adjustable proportioning valve to throttle down the rear brake line pressure. This careful tuning is required to ensure the rear wheels do not lock up before the front wheels.
2001-02 Vipers have a 43mm diameter single piston rear brake
caliper that is managed by the OEM ABS to prevent rear wheel
lockup. Gen 3 and Gen 4 Vipers with four-piston rear brake calipers also
have mechanical and electronic systems to manage the brake balance.
Simply, all larger calipers move the braking bias towards the rear wheels and if too large, the adjustable proportioning valve or ABS moves the balance back into the "sweet spot." The 40mm rear calipers provide a more calculated solution by moving the brake balance performance directly to the "sweet spot" without any adjustment.
Picture modified from an original Stoptech document, Stoptech does not endorse this version.