The Brake Proportioning Valve on your Patrol controls the amount of rear brake that is applied when you put your foot on the brake pedal. The higher you lift your Patrol the less brake is applied. The system itself is a great one, and ensures that if your vehicle is loaded for towing , and the back is lower, more rear brake is applied. To retain the standard brake bias on a lifted Patrol, Roadsafe have a simple bracket extension to reposition the Brake Proportioning Valve.