22 fastlane
fast
FIGURING OUT DRAG
RACE AND STREET-STRIP
SHOCK
ABSORBERS
The shock absorber is a key ingredient in
making a car “work” on the street or on the
strip. The reason for this is simple: if you
can control the wheel motion, then you can
control the dynamics of the car. In the world
of acceleration, this boils down to “hook.” It
also means your tuning capabilities are greatly
expanded.
Shock Basics
Let’s start at the beginning. A shock is a hydraulic
device that resists chassis movement by passing
oil through a set of orifi ces and valved passages.
A shock extends and compresses as the car moves
– in the shock world, these movements are termed
rebound and bump.
Rebound (extension) 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. As the car is pushed up and
forward, the axle housing sees the opposite force
(don’t forget the tire sidewalls are also wrapping
up). As the car moves forward, torque is created as
the tires get traction.
Too much body separation can lead to some
undesirable side eff ects:
•
Wheel hop can occur as the tire tries to return
to its original form (the tire unwraps). Stiff ening
the shock’s rebound can control wheel hop.
•
Tire shake is similar to wheel hop and can be
addressed similarly.
For the most part, a “bald” starting line or
unprepared surface will mandate a softer rebound
setting to apply the tires with more force. A stiff er
rebound setting on a well-prepped track can
provide quicker vehicle reaction times. Essentially,
too much separation is an ET and energy waster.
Bump (compression) is the shock’s resistance
to the chassis moving down or the axle housing
moving up or into the chassis. The bump
adjustment is important since it determines how
long the tires are held down on the track after
chassis separation. When you use a soft rebound
setting on a double adjustable shock, try using a
slightly stiff er compression setting.
To get a grasp of what this is all about, pretend
that you drive your car over a good old-fashioned
speed bump. The speed bump “bumps” the shock
and compresses it. After you drive over the speed
bump, the shock rebounds and extends. That’s
where you get the terms “bump” and “rebound”.
There are all sorts of shock absorbers
built for street-strip and drag race
applications. This is a complete set
from Strange Engineering. The fronts
are single-adjustable while the rears
are double-adjustable.