What is an adjustable proportioning valve?
  A proportioning valve controls the rate of increase in pressure rise to the rear brakes as they are applied. In simple terms, it reduces the pressure supplied to the rear brakes to help keep them from locking up as weight transfers from the rear tires to the front tires under deceleration. An adjustable proportioning valve gives you the ability to change the pressure at which the decrease in rear line pressure occurs (“knee point”) relative to the front line pressure to suit your vehicle setup and driving style.
