knightshift- droop is the down travel of the arms. In other words, as you lift the chassis of your car up, it is the amount of travel before the tires come off the ground. If the car sits at ride height, and you lift the back end of the chassis, and the tires leave the ground when you lifted the car 5mm past ride height, you have 5mm droop. Droop lets the chassis roll around and it lets the wheels drop down into imperfections in the track.