A swing-arm suspension has...
A swing-arm suspension has a large motion ratio that causes the shock shaft to move at about 70 percent of the speed of the wheel in vertical displacement. That means if we install a "4" shock, it may well behave like a "3" shock would in a one-to-one installation because the shaft is moving slower than the vertical speed of the wheel.
Once we have that, we can use the LR shock to enhance turn-exit performance. By using split valve shocks, we can increase the compression of the LR shock and, at the same time, maintain a more moderate rebound rate to enhance turn-exit performance without messing up the entry performance.
Remember we softened the RR shock compression to effect the same improvement. When we increase the LR shock compression and decrease the RR shock compression, we have used two corners of the car to improve exit performance.
On dirt or asphalt, we can look at the compression and rebound rates on the left side of the car to effect the overall attitude of the car.
Lower overall compression for asphalt or dirt cars on high-banked tracks will allow the left side of the car to compress more quickly and enhance aero downforce. Once the LF corner is down and the aero effect is enhanced, more downforce will keep the left side down after the effect of the movement of the shocks is over. Very stiff overall left-side compression is never desired.
Stiff overall rebound on the left side of the car helps to maintain the aero effect when coming off the corners by reducing the tendency for the left side to lift as we accelerate. This helps to continue the low left-side attitude that creates high aero downforce.
All of the above is related to asphalt tracks or even dirt tracks with high banking and a higher degree of traction. We need to think a lot differently when dealing with shocks for dry, slick dirt tracks. The trend has been to allow the car to jack up on the left side. A very low setting for rebound on the left-side shocks allows a sudden and rapid movement of the LF and LR suspensions so the left side of the car is up through the middle.
This attitude promotes weight transfer from the left side to the right side, the theory being that more weight on two tires will bite into the dry slick better than distributing the race car weight among the four tires. The high-left-side attitude does more than promote weight transfer; it allows for more rear steer by causing the LR wheel to swing up and under the forward mounts of the trailing links, and that action steers the rear end to the right.
For dirt racing, we need to also complement the softer left-side rebound rates in our shocks with a lower compression rate for the right-side shocks on flat and dry-slick types of race tracks. This allows the right side to drop quickly on turn entry as the left side rises up.
The soft and slow motion of the shocks at both sides of the car help to reduce the "shock" to the tires during transitional periods of entry and exit. This helps the tire contract patch maintain grip with the racing surface.
As we are always saying, solve your setup problems first before experimenting with shocks. Never crutch a bad setup. Most shock technicians will tell you to put standard rate shocks on the four corners until the setup is sorted out. Make changes to one corner at a time to see and feel the results. The most important task is to make the driver more comfortable, and that will translate to faster lap times.