The suspension system of a vehicle refers to the group of mechanical components
that connect the wheels to the frame or body. A great deal of engineering effort
has gone into the design of suspension systems because of an unending effort to
improve vehicle ride and handling along with passenger safety and comfort. In the
horse and buggy days, the suspension system consisted merely of a beam (axle)
that extended across the width of the vehicle. In the front, the wheels were
mounted to the axle ends and the axle was rotated at the center to provide
steering. The early automobiles used the one‐piece axle design but instead of
being rotated at the center, it was fix‐mounted to the vehicle through springs to
provide the cushioning of shock loads from road inaccuracies. The wheels were
rotationally‐mounted at the axle ends to provide steering. The first springs
consisted of thin layers of narrow pieces of strip steel stacked together in an
elliptical shape and were called leaf springs. In later installations, leaf springs
were replaced by coil springs. In front‐engine rear‐drive vehicles, the front beam
axle was replaced by independently mounted steerable wheels. The wheels were
supported by short upper and lower hinged arms holding them perpendicular to
the road as did the previous axle beam designs. A coil spring was used to support
either the upper or the lower arm to provide dampening. Shock absorbers began
to be used to dampen shock loads and also to provide resistance to spring
oscillations. Later it was learned by shortening the upper arm; wheel tilt (camber)
could be controlled to prevent edge loading tires while cornering. The power
transmitting drive axle in the rear served as the beam‐type suspension with
dampening provided by either leaf or coil springs as well as shock absorbers.  
When front‐engine front‐drive passenger cars were introduced, the upper arm
was rotated up and replaced by a member called a “strut” which contained the
concentrically mounted spring and shock.  This arrangement provided additional
space for transverse mounted engine/transmission modules and the front drive
shaft. This same type of suspension was also used in the rear of many cars. Trucks
continue to be front‐engine, rear‐drive vehicles many of which are using beam‐
type axle suspension systems in both the front and rear. This course will study the
design and application of five currently used suspension systems.

There are three basic types of suspension components: linkages, springs, and
shock absorbers. The linkages are the bars and brackets that support the wheels,
springs and shock absorbers. Springs cushion the vehicle by dampening shock
loads from bumps and holes in the road. Shock absorbers use hydraulic pistons
and cylinders to cushion also the vehicle from shock loads. They also serve to
dampen spring oscillations, thus bring the vehicle back to a neutral position soon
after being shock loaded by a road obstruction.  
Links: There are a number of various shaped links that are used for the different
types of suspension systems. They vary from straight bars to forged, cast or
stamped metal shapes that best fit to support the springs, shocks and wheels
onto vehicle frames or body structures. The simplest linkage is a straight bar that
connects one wheel to the other on the opposite side of the vehicle. Others can
be intricately shaped to connect springs, shock absorbers and wheels to vehicles
as explained later.
Springs: There are three different spring types that are used in suspension
systems: coil, leaf and torsion bar. Coil springs are merely wound torsion bars.
They are commonly used because they are compact, easily mounted and have
excellent endurance life properties. Leaf springs are long thin members that are
loaded in bending. They are used as an assembly being comprised of several
layers of thin metal to obtain the correct spring rate. Leaf springs serve as both
the damping member and the linkage. Torsion bars rely on the twist of a long bar
to provide a spring rate to dampen car shock loading. Torsion bars mount across
the bottom portion of a vehicle and are more difficult to package than others.  
Shock Absorbers: Shock absorbers use a piston and cylinder along with adjustable
valves to control the flow of hydraulic fluid to set the damping force in both the
retract (jounce) and extend (rebound) positions. Shock absorbers are set to
retract under a lower force than to extend. This action absorbs road bump forces
and dampens spring oscillations resulting in better vehicle ride and control.