The spring is the core of all suspension systems. It absorbs shock forces while maintaining correct riding height. If the spring is worn or damaged, the other suspension parts shift out of their proper positions and are subject to increased wear.

Various types of springs are used in suspension systems - coil, leaf, air springs, and torsion bar. Springs are mounted in rubber to reduce road shock and noise.

Spring Terminology

Automotive springs are generally classified by the amount of deflection exhibited under a specific load. This is referred to as the spring rate. According to the law of physics, a force (weight) applied to a spring causes it to compress in direct proportion to the force applied. When that force is removed, the spring returns to its original position if not overloaded. Remember that a heavy vehicle requires stiffer springs than a lightweight car.

The springs take care of two fundamental vertical actions: jounce and rebound. Jounce occurs when a wheel hits a bump and moves up. When this happens, the suspension system acts to pull in the top of the wheel, thereby maintaining an equal distance between the two wheels and preventing a sideways scrubbing action as the wheel moves up and down. Rebound occurs when the wheel hits a dip or hole and moves downward. In this case, the suspension system acts to move the wheel in at both the top and bottom equally while maintaining an equal distance between the wheels.

The spring moves back and forth from jounce to rebound. Each time, the movement becomes smaller. This is caused by friction of the spring's molecular structure and its pivot joints. A shock absorber is added to the suspension to dampen the motion of the spring.

All of the vehicle's weight supported by the suspension system is known as sprung weight. The weight of those components not supported by the springs is know as unsprung weight. The vehicle's body, frame, engine, transmission, and all of its components are considered sprung weight. Undercar parts classified as unsprung weight include the steering knuckle and rear axle assemblies (but not always the differentials). Keep in mind that, in general, the lower the ratio of unsprung weight to sprung weight, the better the vehicle's ride will be.

SHOCKS AND STRUTS

A shock absorber is used to control, or dampen, spring oscillations. A strut serves the same purpose as a shock absorber, but it also supports the steering knuckle. Typically, there is one shock absorber or strut at each wheel.

Shock absorbers have three main purposes:

- To control spring action and oscillations to provide the desired ride quality

- To prevent body sway and lean while cornering

- To reduce the tendency of a tire to life off the road, which improves tire life, traction, and directional stability

Since shock absorbers control spring action, spring oscillations, and chassis oscillations, they contribute to vehicle safety and passenger comfort. If the shock absorbers are worn out ,excessive chassis oscillations may occur, particularly on rough road surfaces. These excessive chassis oscillations may result in loss of steering control. Worn-out shock absorbers also cause excessive body lean and sway while cornering, which may cause the driver to lose control of the vehicle. Shock absorbers are extremely important to providing longer tire life, and improving vehicle handling, steering quality, and ride quality.

Shock absorber design is matched to the deflection rate of the spring to control the spring's action.