Droop Suspension Setting
If you are among those that define the droop value as the amount the chassis rises above ride height just as the wheels clear the ground (or, conversely, the amount the wheels droop while keeping the chassis at ride height); then, here is a simple way to calculate and determine the suspension measurement for your desired droop setting taking into account the ride height and the tire diameter.
This suspension measurement is made from the setup board (or similar flat surface) to the centerline of the axle at the wheel hub (same place the wheel mounts), and is equal to the height of the axle centerline above the setup board when the suspension is at the desired droop. Physically this measurement can be easily made with a 6” metal ruler (got one from Harbor Freight for 99 cents, on sale) or similar measuring device that you have in your tool kit, and the suspension is adjusted to the desired value using the droop screws. The adjustments are made in the usual way with the wheels removed, shocks and sway bars disconnected, etc.
Use the following formula to determine the desired measurement value:
(A/2) + B – C – D = E
A = Tire diameter
B = Height of chassis above setup board for measuring purposes
C = Ride Height
D = desired Droop
E = Centerline of Axle at wheel hub (calculated, based on above parameters)
The one variable in the above formula that may not be obvious is “B”. This is the height you raise the chassis above the setup board when the measurements and adjustments are made. If you’re lucky and none of your suspension components extend below the bottom of the chassis at the desired droop then you can place the chassis directly on the setup board and B = 0 in the above formula. Otherwise, the chassis will need to be raised by some means when you make the measurements and adjustments and this amount is entered into the above formula. I personally use Hudy droop blocks, as I happen to have a set, and therefore in the above formula B = the Hudy block thickness.
This method will allow you to easily determine the adjustments to make in your suspension setting to maintain your desired droop when you change your ride height or tire diameter.