The Suspension System
The components of the suspension system perform six basic functions:
- Maintain correct vehicle ride height
- Reduce the effect of shock forces
- Maintain correct wheel alignment
- Support vehicle weight
- Keep the tires in contact with the road
- Control the vehicle's direction of travel
Typically, struts consists of a coil spring to support the vehicle's weight, a strut housing to provide rigid structural support for the assembly, and a damping unit within the strut housing to control spring and suspension movement. The bottom of the strut body attaches to the steering knuckle, which in turn connects to a lower control arm through a lower ball joint.
The top of the strut is connected to the vehicle body through the upper
strut mount, in some cases called a bearing plate. This bearing plate allows
the strut to pivot as the wheels are turned. It must be flexible enough
to handle slight angle changes and dampen movement of the upper end of
the strut. This mount or bearing plate transfers vehicle load to the strut
and spring, making the upper mount/bearing plate the load carrier and the
lower ball joint the follower.
The strut housing holds the damping unit and fluid. It is made of heavy gauge steel so that it is rigid enough to provide structural support and withstand road shock.
The piston rod of the strut is much larger in diameter than the piston rod of the typical shock absorber. This is to withstand the side load on the strut shaft. A strut rod will measure up to 7/8 of an inch in diameter while the piston rod of a typical shock measures up to ½ of an inch in diameter.
A coil spring is located between the upper and lower spring seats. It is held there by tension. The lower spring seat is welded to the strut housing, while the upper spring seat is kept in place by the upper strut mount.
Struts also have a jounce (or compression) bumper located under the upper spring seat. The purpose of this component is to limit suspension travel by not allowing suspension components to hit together.
Finally, a large nut at the end of the strut rod holds everything together.
