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Road racing or circuit racing is competing on a twisting track of left and right turns, either wheel-to-wheel racing or competing for the quickest lap times. Shock absorbers play a key role in road racing and work together with the other suspension components, especially when adjustable to fine tune for optimized body control and handling balance. Road racing corners tend to be longer distances and durations, higher speeds, and with more time spent at peak cornering forces compared to autocross corners.
Depending upon many aspects and variables about the car (sprung and unsprung weight, aerodynamics, higher spring rates, racing vs. street-based tires, etc.), the priority mix of rebound and compression damping can vary. Rebound (extending motion) damping helps control the vehicles sprung and transitional weight and can be fine-tuned to optimize the entire suspension. Compression or bump (compressing motion) damping controls the vehicle’s unsprung weight and essentially helps hold the tire to the ground to maximize tire and surface grip. Cars with significant aerodynamic downforce or extra grippy racing tires will increase the importance of compression damping and tuning.
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. Cars with higher aerodynamic downforce and very grippy racing tires will have increased priority on compression damping. 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 laps 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 longer duration corners spent at higher speeds closer to the limits of adhesion, fine tuning rebound damping for road racing can keep the car cornering at its limits while providing the stability and consistency that driver desires for faster lap times. 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 laps, 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 or 1-2 sweep or click 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 lap times.
3) Repeat this step until the car enters the corners smoothly with no drastic attitude changes and without leaning excessively. Increasing the rebound stiffness beyond this point may be unnecessary and may in fact be detrimental. |