This document was e-mailed to me. It looks like it has some good info, so I'm posting it here. I hope the author's name is right. I took the liberty of changing fonts and correcting a spelling error or two. I don't have the Bilstein setup recommendations he references below. Considering the Bilstein references, he may work for them. Obvoiusly this man is very knowledgable so I didn't change the content!!...Dan Franks (race66)
How To Shock Tune Your Chassis
By David Duensing
Study the current Bilstein set-up recommendations for your particular type of racing. These combinations are tested and proven successful, but due to the many variables that come into play under racing conditions, it is to your advantage to have a basic understanding of how shock damping rates affect your lap times. Adjustments can then be made with reason and understanding.
Simply stated, shock absorbers convert the kinetic energy of the spring movements into heat. This heat is then dissipated into the air through the shock tube or body. In practical application, shock absorbers are necessary to maintain maximum tire patch contact to the track as the car corners and negotiates irregularities on the racing surface.
Spring rates determine how far your chassis rolls, pitches or squats. Shock rates determine the length of time it takes for each of these movements to occur.
Rebound damping controls the movement of that part of the car's sprung mass that is stored in a compressed spring. The rebound damping rate determines how long it takes for the compressed spring to return to the static ride height. The larger the rebound figure, the more the shock resists the compressed spring's effort to rebound, and the longer it takes for the chassis to return to the static ride height.
Compression damping controls only the oscillation of the car's unsprung weight. Therefore, it is normal to use less compression damping than than rebound damping. The exception occurs when we choose to slow the downward movement on a particular corner of the car to mimic the effect of a stiffer spring.
Here are some guide lines to use when shock tuning your chassis at the track or making the best decision during initial set-up. We are making the assumption that you have removed as many variables as possible and are using the best combination of springs, weight, wheel spacers, tire compound, stagger, etc.
Utilizing the "Think Track" below, study the following list of suggestions. These are not rules, not even rules of thumb, but they are tendencies that are more often true than not when racing late models and modifieds on asphalt or dirt.
All you have to do is determine what you want the car to do from entry to exit. Just think it through!
Trouble Shooting The Car On The Track
If your car is:
Loose(Oversteer)from 0 degrees to 45 degrees
Increase compression rate on front. Decrease rebound rate on rear, or only on left rear.
Tight(Understeer) from 0 degrees to 45 degrees
Decrease compression rate on front. Increase rebound rate on rear, or only on left rear.
Loose(Oversteer) from 45 degrees to 135 degrees
Decrease rebound rate on right front. Decrease rebound rate on left rear. Decrease compression rate on rear, or only on right rear.
Tight(Understeer) from 45 degrees to 135 degrees
Increase rebound rate on right front. Decrease rebound rate on left front. Increase compression rate on rear, or only on right rear.
Loose(Oversteer)from 135 degrees to 0 degrees
Decrease rebound rate on front. Increase rebound rate on left rear. Decrease compression rate on rear, or only on left rear.
Tight(Understeer) from 135 degrees to 0 degrees
Increase rebound rate on front. Decrease compression rate on rear.
When analyzing corner entry, or deceleration handling, realize that the chassis is affected by:
Compression rate in front..........&..........Rebound rate in rear.
When analyzing corner exit, or acceleration handling, realize that the chassis is affected by:
Rebound rate in front..........&..........Compression rate in rear.
Bilstein shocks are famous for their superior performance on very rough asphalt or rutted dirt tracks. You may need to choose a shock with more compression damping than found on the set-up-sheets under extreme rough track conditions.
Keep in mind that there are many adjustments on your chassis other than shock absorbers. The oversteer / understeer balance may be affected by stagger, tire compound, wheel spacing, spring rates, sway bar, panhard and others. Shocks can be used to fine tune your chassis to gain that last few tenths of a second on the track.