Brake proportioning valve

[Tom Goldman]

no need for a prop valve on the rear of most race cars with slicks , especially big ones.
As the others have mentioned it's more effective on the front brakes for preventing them from locking up at the stripe.
The Wilwood valve can limit the initial pressure by up to 57% .the pressure will eventually rise to the same pressure being applied to the rear wheels, It's the rate of application that the valve is controlling.