How to use a droop gauge set
Down Stop Method
In order to have a balanced car left and right, suspension heights should be equal. Setting your down stops equal between sides is important in setting up your car. In order to measure the down stop adjustment of your car, you will need to place your car onto the support blocks at the lower level (6mm) on a flat level surface with the wheels off. Make sure the car sites flush on the support blocks. Slide the droop gauge underneath the lower arm until it touches the outside edge of the lower suspension arm. Use the numbers on the top of the gauge to determine the height of your lower suspension arms. Screw in the down stop to raise the lower suspension arm to the desired height or out to lower it. Make sure left and right suspension arms are set equally. Lowering the suspension arms will increase droop while raises them will decrease droop as long as preloads remain the same.
Droop is the amount of sag a suspension has when the wheels are loaded by the weight of the car (springs are compressed). It can also be defined as the amount of upward travel a suspension has before the wheels lift off the ground (springs become unloaded). Droop can therefore be measured by finding the difference between the ride height of your car when it is loaded verse unloaded. To find the loaded ride height of your car place it on a flat level surface and measure the ride height of the bottom chassis plate near the desired wheel using the MC3-WLS ride height gauge. To determine the unloaded ride height of your car, place your car on the 8mm support block (taller side) on a flat level surface. Make sure the car sits flush on the support blocks. Then, using the droop gauge, slide it under the wheel until it touches the wheel. Use the numbers on the side of the gauge to determine the unloaded ride height. The amount of droop is the difference between the two numbers. For example, if your ride height is 2.4mm loaded and 3mm unloaded you have 0.6mm of droop. For accuracy, both left and right tires should be equal in diameter. To reduce droop (less sag) on one side of the car you must increase the preload on that sides spring/shock. To increase drop (more sag) you must reduce the preload on that sides spring/shock.
For most RWD cars, a standard setup on RCP tracks is to have 0 to 1mm of droop in the front and 1 to 2mm of droop in the rear. As a general rule, adding more droop to one end of the car will provide more grip to the opposite end. For example, if you have too much grip on corner entry, reducing rear droop will allow the front end to push (understeer). As always there is a limit. For example, having 0 droop in the rear is not recommended as this will prevent the rear from absorbing bumps resulting in less rear grip.