Suggested Adjustment Procedure for Autocross Use

Autocross is a popular form of motorsport with drivers competing for the fastest times running one-car-at-a-time through a very tight course of cones with strong emphasis on driver skill, speed, precise vehicle placement, and body motion control in tight corners and transitions.  Shock absorbers play a key role in autocross car control, especially when adjustable to tune for optimized body transitional control and handling balance. In autocross, the corners are often very tight with short duration and the car has very quick transitions from initial corner entry to peak cornering force and back to chassis level under acceleration at corner exit so optimizing body transitional control is critical in improving run times. In autocrosses with long slaloms of connected left-right-left-right vehicle body weight transitions, proper shock tuning can have a big impact on smoothness, flow, and speed.

For autocross, the primary shock tuning tool is adjustable rebound (extending motion) damping that helps control the vehicles sprung and transitional weight.  The secondary shock tuning tool is compression or bump (compressing motion) damping which controls the vehicle’s unsprung weight and essentially helps hold the tire to the ground to maximize tire and surface grip.

The tuning tips below start with compression damping first and then go to rebound damping for cars with Double Adjustable shocks.  For cars with Single Adjustable (adjustable rebound damping with preset compression damping), please skip straight to the rebound tuning tips.
Adjusting the Compression (Bump) Damping Control
Compression or Bump damping controls the unsprung weight of the vehicle (wheels & tires, brakes, axles, etc.) and helps optimize the grip between the tires and surface. It controls the upward movement of the suspension such as hitting a bump in the track surface. Compression damping should preferably not be used to control the downward movement of the vehicle when it encounters dips or control body roll in side-to-side transitions.  Don’t try to hold the car up with compression damping (that is the job of the springs) but instead hold the tire down to the surface to maximize grip.

1) Set all four dampers at or near minimum bump and minimum rebound settings. Drive one or two runs to get the feel of the car and focus on tire grip and responses over bumps.  Disregard body lean or roll and concentrate solely on how the car feels over bumps looking for the threshold where the car "walks", “skates” or "side-hops" on the roughest turn or biggest bump.

2) Increase bump adjustment 2-3 clicks on all four dampers and drive the car again. As the compression damping increases, the car’s initial turn-in should become sharper, the tire carcass and sidewall works harder, etc.  Repeat this step until the car starts to feel harsh or loses grip over bumps. Back off the bump adjustment 1-2 clicks and the bump adjustment is completed for that surface and tire combination. NOTE:  You may reach the back-off point sooner on one end of the vehicle than the other. If this occurs, keep increasing the bump adjustment on the still gripping end until it too feels too hard or loses grip. Then back that side off 1-2 clicks. 
Adjusting the Rebound Damping Control
Rebound damping controls the car’s sprung weight and body transitional roll (lean) as when entering or exiting a turn. Rebound damping does not limit the total amount of roll; it limits how fast the total roll angle is achieved. How much the vehicle leans is determined by other things such as spring rate, sway bars, roll center heights, etc.
In most cases, too much rebound damping on either end of the vehicle will cause an initial loss of lateral acceleration (cornering power) at that end and can cause the vehicle to oversteer or understeer excessively when entering or exiting a turn.  With the extremely tight turns of autocross, some amount of overdamping can sometimes be useful to help the chassis rotate more quickly, especially in generally stock suspension, softly sprung cars and front wheel drive cars.  Primary rebound tuning emphasis is normally on rear shocks for corner entry and front shocks for corner exit, controlling body roll and chassis rotation to meet the driver’s handling balance preferences, confidence, and experience levels. Tune from corner entry, through mid-corner and corner exit.
1) With the rebound set in the lower to middle part of the adjustment range, drive the car one or two runs, paying attention to how the car rolls and the chassis rotates when entering and puts power down when exiting a turn.

2) Increase rebound damping in ¼ to ½ turn increments on all four dampers and drive the car again to feel and judge the changes of roll, balance, rotation, and power application grip. If one end of the car slides excessively at corner entry or exit, soften the rebound slightly at the sliding end to return to driver’s preference and quickest run times.