PURPOSE OF THE SUSPENSION SYSTEM

As we review suspension system components and how they work together, remember that a vehicle in motion is more than wheels turning. As the tire revolves, the suspension system is in a dynamic state of balance, continuously compensating and adjusting for changing driving conditions. Today's suspension system is engineering at its best.

The components of the suspension system perform six basic functions:

1. Maintain correct ride height
2. Reduce the effect of shock forces
3. Maintain correct wheel alignment
4. Support vehicle weight
5. Keep the tires in contact with the ground
6. Control the vehicle's direction of travel

However, in order for this to happen, all the suspension components, both front and rear, must be in good working condition.

MAIN COMPONENTS OF A MODERN SUSPENSION SYSTEM

At this point, it's important to understand that the main components of a moving vehicle suspension system are the Shock Absorbers, Springs and Tires. We will first turn our attention to the design and function of springs. In the following section we will thoroughly examine the function and design of shock absorbers.

The springs support the weight of the vehicle, maintain ride height, and absorb ground shock. Springs are the flexible links that allow the frame to ride relatively undisturbed while the tires and suspension follow the bumps in the ground.

Springs are the compressible link between the frame and the body. When an additional load is placed on the springs or the vehicle meets a bump in the ground, the springs will absorb the load by compressing. The springs are a very important component of the suspension system that provides ride comfort. Shocks help control how fast the springs and suspension are allowed to move, which is important in keeping tires in firm contact with the ground.

During the study of springs, the term bounce refers to the vertical (up and down) movement of the suspension system. The upward suspension travel that compresses the spring and shock absorber is called the compression. The downward travel of the tire and wheel that extends the spring and shock absorber is called rebound, or extension.

When the spring is deflected, it stores energy. Without shocks the spring will extend and release this energy at an uncontrolled rate. The spring's inertia causes it to bounce and overextend itself. Then it re-compresses, but will again travel too far. The spring continues to bounce at its natural frequency until all of the energy originally put into the spring is used.

If the shock absorbers are worn and the vehicle meets a bump in the road, the vehicle will bounce at the frequency of the suspension until the energy of the bump is used up. This may allow the tires to lose contact with the ground.

Shock absorbers that are in good condition will allow the suspension to oscillate through one or two diminishing cycles, limiting or damping excessive movement, and maintaining vertical loads placed upon the tires. This helps keep the tires in contact with the ground.


SPRING DESIGNS

Before discussing spring design, it is important to understand sprung and unsprung weight. Sprung weight is the weight supported by the springs. For example, the vehicle's frame and motor would be sprung weight. Unsprung weight is the weight that is not carried by springs, such as the tires, wheels, and brake assemblies.

The springs allow the frame and vehicle to ride undisturbed while the suspension and tires follow the grounds surface. Reducing unsprung weight will provide less road shock. A high sprung weight along with a low unsprung weight provides improved ride and also improved tire traction.


Coil Springs
The most commonly used spring is the coil spring. The coil spring is a length of round spring steel rod that is wound into a coil. Unlike leaf springs, conventional coil springs do not develop inter-leaf friction. Therefore, they provide a smoother ride.

The diameter and length of the wire determine the strength of a spring. Increasing the wire diameter will produce a stronger spring, while increasing its length will make it more flexible.

Spring rate, sometimes referred to as deflection rate, is used to measure spring strength. It is the amount of weight that is required to compress the spring 1 inch. For example: If it takes 100 lbs. to compress a spring 1inch, it would take to 200 lbs. to compress the spring 2 inches.

Some coil springs are made with a variable rate. This variable rate is accomplished by either constructing this spring from materials having different thickness or by winding the spring so the coil will progressively compress at a higher rate. Variable rate springs provide a lower spring rate under unloaded conditions offering a smoother ride, and a higher spring rate under loaded conditions, resulting in more support and control.

Coil springs require no adjustment and for the most part are trouble-free. The most common failure is spring sag. Springs that have sagged below vehicle design height will change the geometry. This can handling problems and wear other suspension components. During suspension service it is very important that vehicle ride height be measured. Ride height measurements not within manufacturer's specifications require replacement of springs.