Basic Principles of Suspension System

The components of the suspension system, while impor tant separately, must operate as a whole for the system to provide all of the requirements during normal driving conditions. As stated before, the suspension is responsible for carrying vehicle weight, absorbing road shocks, providing a smooth ride, and allowing good handling qualities.

While many drivers do not know the specifics of how these goals are met, they do feel how their vehicle rides and handles and can tell quickly when something is not quite right. For the technician, it is important to under¬ stand the underlying principles of suspension operation so that he or she can accurately diagnose a concern when one is present.

Oversteer.

Oversteer is a term used to describe a driving condition where the rear tires reach their cor¬ nering limit before the front tires. This can allow the rear tires to break loose and cause the vehicle to spin. Figure 6-10 illustrates the effects of oversteer. Oversteer can be used as an advantage in certain racing situations, but if you have ever experienced the back end of a car sliding on wet or slippery pavement, you know that over¬ steer can also be a very undesirable event!

To correct for oversteer, you should steer into the slide and reduce power until control returns. Applying the brakes can actually make oversteer worse since the weight transfer from the rear wheels can reduce rear tire traction.

Understeer.

The opposite of oversteer is understeer. This condition occurs when the front of the vehicle can¬ not make a turn through the desired turn radius because the front tires have lost traction. Figure 6-11 shows how a vehicle will continue in a somewhat straight line instead of making the intended turn. This causes the vehicle to overshoot the turn. If you have ever tried to make a turn in slippery or snowy conditions and the vehicle contin¬ ued in a straight line instead of turning the corner, you have experienced understeer. Understeer is measured by the difference between the angle the tires are pointing and the angle needed to make the turn. Most cars are designed to have understeer. This is because understeer can be reduced by reducing vehicle speed, which is safer for the average driver.

Neutral Steering.

If a vehicle turns at the same rate that the steering wheel is turned, it is said to have neutral steering. This means that the vehicle does not exhibit a tendency to either over- or understeer.