The suspension system includes the various shocks, struts, linkages, etc. that connect the chassis to the wheels of the vehicle. It serves two major purposes. First, it ensures the wheels maintain contact with the road surface, providing consistent traction. Second, it provides a comfortable ride for passengers as the vehicle navigates turns, rolls over imperfections in the road, encounters bumps, and so forth. These objectives are contradictory however (one relies upon downward force, the other upward) so suspensions are specifically configured to balance these goals.
The springs serve to support the weight of the car evenly; compressing and rebounding to compensate for anything encountered beyond a completely flat road surface. There are various styles of springs to accommodate different vehicle types. The three major kinds are coil springs, leaf springs, and torsion bars. Coil springs and torsion bars are usually installed in the front while leaf springs are more useful in the rear of the vehicle.
In the past, a wide variety of direct and indirect shock absorbing devices were used to control spring action of passenger cars. Today, hydraulic or gas shock absorbers and struts are the norm.
Another component of the suspension system is the sway bar. Some cars require stabilizers to steady the chassis against front-end roll and sway on turns. Stabilizers are designed to control this centrifugal tendency that forces a rising action on the side toward the inside of the turn. When the car turns and begins to lean over, the sway bar uses the upward force on the outer wheel to lift on the inner wheel, thus keeping the car more level.
The primary job of the control arms is to mount the suspension to the frame or body of the vehicle and to allow the suspension to move and keep it in its proper place. They come in all shapes and sizes and are specifically designed to maintain the geometry of the suspension in a wide range of movement. The most common problem is that the bushings at the body mounting points wear out causing unwanted movement and/or a terrible squeaking noise.