this might help
Droop is sometimes associated with downstop. This is both correct and incorrect.
Droop refers to the amount that the chassis travels downward after the car is dropped
and the wheels touch the ground; it is also the amount that the chassis travels upward
before the wheels lift from the ground.
Droop is in large part affected by the downstop setting, but is also affected by ride height
adjustment.
• A higher downstop setting creates a smaller gap between the downstop setscrew and
the chassis at rest. This smaller gap reduces the amount that the chassis rises before
the wheels lift from the ground. The result is a smaller droop value.
• A lower downstop setting creates a larger gap between the downstop setscrew and
the chassis at rest. This larger gap increases the amount that the chassis rises before
the wheels lift from the ground. The result is a larger droop value.
INITIAL STEPS SET-UP COMPONENTS:
Prepare the car as follows: Use the following set-up components:
• Shocks: Attach the front and rear
shocks.
• Anti-roll bars: Attach front and rear
anti-roll bars.
• Wheels: Attach the wheels. Both left
and right wheels at the front or rear
should be the same diameter.
• Small ruler
MEASURING DROOP
You measure droop with the car ready-to-run.
1. Place the car on the set-up board.
2. Push down and release the front and
rear of the car so that the suspension
settles.
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3. Place the ruler vertically beside the
chassis, so that you can see how much
distance there is between the flat surface
and the bottom of the chassis.
4. Keeping the ruler in place, slowly lift the
chassis at its centerline. The chassis rises
slightly until the wheels just lift from the
set-up board.
5. On the ruler, note the distance to the
chassis bottom. The amount that the
chassis rose before the wheels lifted is the
droop value.
6. Repeat steps 3-5 for the other end of
the car.
7. Adjust downstops to change the droop
values.
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DROOP AND RIDE HEIGHT
When you use rubber tires on your car, you can set a particular downstop value to get
a particular droop value, and then forget about it. Rubber tires do not wear appreciably
during use, so the droop value should not change.
However, when you use foam tires on the car, things become a bit more complicated. You
will have to constantly adjust ride height and downstop settings to maintain a particular
droop value.
Consider the following situation:
You have foam tires of a particular diameter. You have adjusted your downstop settings
and your ride height settings. There is 2mm of front droop and 1mm of rear droop.
After you race the car for a short time the foam tires wear down to a smaller diameter,
which decreases the ride height. So you now adjust the shock spring preload to
increase the ride height to a proper value again.
Increasing the ride height causes the chassis to raise up slightly, which decreases the
amount of space between the downstop screws and the chassis. The result is that the
droop values are now reduced, so the car will handle differently.
(In extreme cases when you have to increase the ride height a lot, the droop may
completely disappear as you increase shock spring preload. If you increase the spring
preload so much that you remove all droop, the ride height will not increase no matter
how much preload you set since the downstop screws are tight against the chassis and
do not permit the chassis to rise).
In this situation, to maintain a certain amount of droop you need to loosen the
downstop screws slightly as you increase the ride height. You must alternate between
adjusting ride height and downstop settings to maintain a particular droop value. This
must be done equally on left and right sides of the car.
ADJUSTING DROOP
You adjust droop by adjusting downstops. To increase the droop value, decrease the
downstop setting. To decrease the droop value, increase the downstop setting.