The use of shock travel indicators...
The use of shock travel indicators can tell us how much total movement we are getting at each corner. It is especially helpful to be able to record both compression and rebound movement. Indicators attached to the shock shaft only record compression movement. To "see" movement at specific points on the race track requires a data acquisition system installed in the car. Later, the team can view the shock speeds and amount of travel at specified points on the racetrack.
Excess movement of the RF corner on entry usually causes the car to push due to excess and sudden camber change at the RF wheel. There's a problem with trying to solve a push like this with a stiffer compression shock. Once we do that, we have further tightened the car by momentarily adding wedge to it. Upon braking, a high-compression RF shock will cause a greater amount of the unsprung weight to be carried by the RF and LR tires, which increases the crossweight in the car, still making push.
Excess movement at the RF can be controlled more effectively by adding an antidive design to the RF and the LF suspensions. Antidive works well to control excess dive on entry while braking and does not affect the setup at any other point on the racetrack.
We can introduce antidive to both front corners of the car so that resistance to dive is distributed onto both front tires. This eliminates the change in crossweight percentage that might make the car tight, as when using a stiff-compression RF shock.
The right-rear (RR) corner experiences the most movement on the race car. Shocks control the speed of this movement so that we can utilize it to effect changes to the weight distribution of the car while the shocks are in motion. Since the RR moves so much, we can do more with it than at any other corner.
Shock angle affects the speed...
Shock angle affects the speed at which the shock moves. If the wheel is moving at 6 inches per second, the shock, if mounted at 20 degrees, will move only 5.47 inches per second.
Rarely do we see teams try to crutch the car using different shocks on the RR corner. Suggestions to change the shock on the RR to solve tight or loose middle handling conditions should be disregarded.
Mid-turn is mostly a steady condition, which means the four corners of the car are holding steady and not moving quickly or a significant distance. If a shock is not moving, it is not affecting the setup or weight distribution on the four tires. Shocks must move to affect the handling of the race car.
On entry, we might want to increase the rebound rate on the RR (in conjunction with the LR shock) to help keep the car's center of gravity lower so less weight transfer will occur from the rear to the front of the car. By causing less weight transfer, we maintain more weight on the rear tires and a more even weight distribution on all four tires in combination, which gives us more traction for enhanced braking. The faster we stop, the deeper we can go into the corner.
On exit, we can enhance bite to help control wheel spin as power is applied to the rear wheels. Using a softer compression shock at the RR will momentarily increase the load on the RF and LR tires while the shock is compressing and weight transfers to the rear on acceleration. The increased crossweight percentage tightens the car at the critical moment of throttle application when we need to stop the tendency of the rear wheels to break loose. An example of a crutch would be increasing the RR compression to loosen a car that is tight off the corner. Most likely the car is tight off because of spring related setup problems or steering problems, not because of the RR shock.
The installed motion ratio...
The installed motion ratio as well as shock angle affects the shaft speed of the shock compared to vertical wheel speed. This directly affects the rate of the shock because shock resistance is determined by the speed that the shock shaft is moving and how quickly the fluid in the shock is forced to move through the valving and bleed holes. The shock will always move slower than the wheel in vertical displacement.
Example: Using a RR spring that is too soft will cause excess travel at the RR corner. We might be tempted to increase the compression at that corner to help control the movement, when the real problem is the soft spring. That corner will still move excessively with the soft RR spring, but it will take longer to get there by increasing the compression rate.
The left-rear (LR) shock may be the most abused shock on the car as far as crutching is concerned. By far, the most common shock crutch is increasing the rebound in the LR shock to attempt to eliminate a "tight in" condition.
The car is probably tight in because of front end geometry problems, causing the front of the car to have no grip. When we increase the rebound of the LR shock, we promote weight transfer off that corner, which de-wedges the car. We now have two ends of the car that have less grip. We have effectively balanced the car at the expense of performance.
Neutral handling is not necessarily related to performance. Overall grip on the four tires is what creates performance by allowing more speed into and through the corners. What we really need is a properly designed front end that will turn in and through the middle so we don't have to crutch the LR shock rates.