 Struts
What
is Ride Control | Vehicle
Dynamics | Suspension
System | Shock
Absorbers | Struts
| Terminology
WHAT IS A STRUT
 Now that we have a more thorough
understanding of shock design, let's focus on the strut.
The strut is a common damper type used on many of
today's independent suspension, front wheel drive
vehicles as well as some rear wheel drive vehicles.
A strut is a major structural part of a
suspension. It takes the place of the upper control arm
and upper ball joint used in conventional suspensions.
Because of its design,
 a strut is lighter and takes up less
space than the shock absorbers in conventional
suspension systems.
Struts perform two main
jobs. First, struts perform a damping function like
shock absorbers. Internally, a strut is similar to a
shock absorber. A piston is attached to the end of the
piston rod and works against hydraulic fluid to control
spring and suspension movement. Just like shock
absorbers, the valving generates resistance to forces
created by the up and down motion of the suspension.
Also like shock absorbers, a strut is velocity
sensitive, meaning that it is valved so that the amount
of resistance can increase or decrease depending on how
fast the suspension moves.
Struts also perform a
second job. Unlike shock absorbers, struts provide
structural support for the vehicle suspension, support
the spring, and hold the tire in an aligned position.
Additionally, they bear much of the side load placed on
the vehicle's suspension. As a result, struts affect
riding comfort and handling as well as vehicle control,
braking, steering, wheel alignment and wear on other
suspension components, including tires.
STRUT COMPONENTS
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.
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