the way back machine switch. In what seems like
the not-so-distant past, it wasn't uncommon
for drag racers to swap the front shocks for
something that was either worn out or had the
fluid drained. Out back something stiff from
a big, heavy car was often used. Today, shock
absorbers are available in countless configurations.
They range from simple, inexpensive single adjustable
models all the way up to three way or electric
adjustable shocks. With today's shocks, one
is given the opportunity to control the wheel
motion. In turn, one can pretty much control
the dynamics of the racecar.
Let's Start At The Beginning...
What really is a shock and what does it do? AFCO explains, "A shock is a hydraulic
device that dampens or resists chassis movement
by passing fluid (oil) through a set of orifices
and valved passages. In an adjustable shock,
manipulating the fluid movement through the
valving of the shock changes the dampening characteristics
- basically softness and stiffness. The range
of softness to stiffness is an important consideration
when evaluating the quality of a shock absorber.
A shock with a broad adjustment range will give
more for the buck, because a broad adjustment
range will give more opportunity to find the
optimum setting for the chassis."
"Rebound is the shock's resistance to being
pulled apart. It can be used to control chassis
separation, the point at which the axle housing
is pushed away from the chassis and the tires
are applied to the track. During separation,
many things occur. Vector forces push up and
forward -- and the axle housing sees the opposite
force (remember that the tire sidewalls also
wrap up). As the car moves forward, torque is
created as the tires create traction to start
this movement. Excessive separation can lead
to some undesirable side effects. For example,
wheel hop can occur as the tire tries to return
to its original form (the tire unwraps). Stiffening
the rebound can control wheel hop. Tire shake
similar to wheel hop and can be addressed similarly.
As a rule of thumb, a bad or 'bald' starting line
will require a softer rebound setting to apply
the tires with more force. A good starting line
can use a stiffer setting, as inherent traction
exists and a stiffer rebound setting provides
quicker vehicle reaction times; excessive separation
only wastes time and energy."
"Compression (bump) is the shock's resistance to the chassis moving down or
the axle housings moving up or into the chassis. The compression adjustment is
an important setting, as it determines how long the tires are held down on the
track after chassis separation. When a soft rebound is selected, a rule of thumb
seems to be to use a slightly stiffer compression setting, so as to control the
rebound of the tire. Track testing can determine the correct setting."
So Far So Good...
Where does one begin? It all depends upon how sophisticated the car is and
how deep your pockets are. At the very least,
a racecar should be equipped with a shock that
allows basic valving changes. A good example
of this is something like the three-way adjustable
Competition Engineering shock absorber.