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
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
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
- To control spring action and
oscillations to provide the desired ride quality
- To prevent body sway and lean
- To reduce the tendency of a tire
to life off the road, which improves tire life, traction, and directional
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.