Car Suspension Related to Over & Under Steer
Over steer and under steer are two often misunderstood concepts related to the way a car handles. The following explanations and diagrams should clear up any confusion you may have.
Over steer is when the rear wheels are carving a larger arc than the front wheels or the intended line of the turn. Rear "slip angles" exceed those of the front tires. This is often described as a "loose" condition, as the car feels like it may swap ends, or be "twitchy." This condition can be caused by "power over steer", where you need to reduce power in order to bring the back end back into line.
Under steer is when the front wheels are carving a larger arc than the rear wheels. This is often described as "push" or "pushing" - as the front end feels like it is plowing off of a corner. Further acceleration only compounds the push, as weight shifts back to the rear drive wheels off of the front turning wheels, leading to a further lessening of the car's ability to turn in. Under steer can be remedied by slight modulation in throttle to transfer weight forward to the front wheels, aiding their traction and ability to carve the turn. Many cars are designed to have a tendency to under steer. If the driver gets uncomfortable and "lifts" off the gas, that will cause the front end to tighten the curve - a relatively safer, and more predictable condition. When the car's body leans in a corner, the outside suspension compresses and the inside suspension extends. In other words, the outside suspension moves in bump direction and the inside suspension moves in rebound direction.
Tuning Tips of your car suspension
If the car rolls on the rear outside suspension during corner exit, increase rebound damping force at the front inside. The front inside suspension affects the car mostly on corner exit. By adding rebound damping you will loosen the car up on corner exit.
If the car rolls on the front outside during corner entry, increase rebound damping on the rear inside suspension.
By adding rebound damping to the front on both sides equally, it will tighten the car some. By adding rebound damping to the rear on both sides equally, it will loosen the car up some.
Note that the shock absorbers do not change the amount of weight transfer, only the time it takes to transfer this weight.
Only adjust enough rebound into each shock absorber to eliminate the undesirable characteristic. Adjusting too much rebound may mask a handling problem of another sort and may even be make things worse and dangerous.