for bad runs vary from driver to driver and from race to race. While
many factors may at one time or another be responsible for creating
inconsistent performances, commonly the problem can be traced to
Drag racers are always searching for the right combination for a
winning run. For various reasons, shocks are overlooked-- more so
in drag racing than in other forms of motorsports. Maybe the flow
of information from the pros down through the ranks is slow or incomplete,
or maybe the racers who perform well don't want to share their secrets.
Product differences may also be a factor. Often racers at the top
level are using products that are not readily available or affordable
to the average drag racer. Whatever the reason, racers often try
to tune a car by replacing the tires, changing the tire pressure,
changing their leave RPM, or detuning their engines to achieve the
desired results at the starting line. Sometimes the desired results
are never found. Perhaps they could be found with proper attention
Shocks can make an incredible difference in a race car's performance.
Too often though, they are ignored as a viable tuning aid. The majority
of drag shocks being used today are old, outdated, and in need of
rebuilding. With regularly scheduled upgrades and rebuilds, an older
set of shocks may perform reasonably well. Keep in mind, however,
that unless they are properly maintained, an old and worn out set
of shocks can have a negative effect on performance.
Shocks that perform well can and will enhance the performance of
the chassis. This doesn't mean that shocks will cure every chassis
problem. The entire suspension system has to perform well. But accurately
adjusted shocks can improve the performance of the car. That performance
improvement can often be the difference between making clean, consistent
runs that result in round wins and making erratic passes that result
in a loss or a DNQ. In short, a high quality adjustable shock will
improve your racing.
The main focus of the current AFCO drag shock program is the adjustable shock, available in both single and double adjustable models. But before we talk about these revolutionary products, let's quickly review some basic shock information.
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 -- softness and stiffness. The range of softness to stiffness is an important consideration when evaluating a shock's quality. A shock with a broad adjustment range will give more bang for the buck, because a broad adjustment range will give more opportunity to find the optimum setting for the chassis. Dyno testing has proven that AFCO's shocks offer one of the widest adjustments ranges in the industry.
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 the chassis up and forward -- and the axle housing sees the
opposite force, the tires become compressed and the sidewalls 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 if excessive separation
has occurred. Tire shake is 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 sitffer 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.
This brings us to AFCO's innovative Velocity Sensitive Valving. This system can enhance performance in many ways. This valving package is extremely sensitive to the speed at which the shock piston is moving. At the starting line, because of the intersection point, engine torque, gearing, tires, center of gravity relative to ground, the shocks will see the highest shaft or piston speeds. To control the suspension, the shock needs to be stiffer at the launch than down track. The AFCO shocks with their new valving actually react more stiffly when needed at the launch yet stay softer for riding the track's irregularities down track. Also, this new valving system is extremely sensitive to chassis tuner input: small changes in the valving will make a noticeable change in the performance of the chassis.
WHY MOUNT A SHOCK UPSIDE DOWN?
AFCO shocks can be mounted upside down to reduce unsprung weight which is anything not bolted solid to the chassis. If the race car were lifted by the main rollcage, anything that would hang down would constitute unsprung weight. Examples would be the wheels and tires, the axle housing, struts, and shocks. Reduction in unsprung weight can promote quicker ET's and extend the life of the race car's components. Also, the reduction of unsprung weight should reduce the chance of wheel hop or tire shake. The momentum of the axle housing (less is good here) will determine whether the tire becomes disturbed and loses traction. Decreasing the mass will give the shock a better chance to control the axle housing during separation, will allow the use of softer shock settings, and will produce quicker runs.
TWO TYPES OF ADJUSTABLE SHOCKS
A single adjustable shock is typically adjustable in only one direction.
However, variations of this type of shock are currently on the market.
The AFCO single adjustable shocks are only rebound (extension)
adjustable. This style of shock is offered because much of the tuning
can be made with only the rebound (extension) of the shock. The
compression (bump) valving is preset at the factory. But don't worry--the
compression (bump) valving is sophisticated. It is also velocity
sensitive, responding to input ranging from a 13 (thirteen) second
street machine to a door slammer running deep into the 9 (nine) second
A double adjustable shock allows compression (bump) and rebound
(extension) to be adjusted separately. This shock is the top of
the line and will allow the maximum performance to be squeezed from
the given combination, provided the chassis tuner has properly adjusted
the shocks. An example of when a double adjustable shock can be
used to enhance performance is when the starting line is less than
ideal. The chassis tuner can soften up the rebound setting to apply
the tires more quickly and with more force. The chassis tuner may
also want to stiffen the compression (bump) setting to hold the
tires on the track, thereby eliminating wheel slippage and also
possible tire shake or wheel hop.
Shocks are just one of many suspension variables on a race car. However, a current trend is to focus on the importance of the effects of shocks on the performance of a race car. With this in mind, we have included a few tuning tips and observations about our series shocks.
Virtually every car will separate at the launch. The rear suspension
system forces the chassis upward while pushing the axle housing
down. This is typically the first movement for most drag cars. For
this reason, the extension, or rebound control, of the shock is
extremely critical. The chassis tuner will need to have a shock
that has a broad range of adjustments--a shock that will make a
noticeable change in suspension characteristics when the shocks
The key elements to tuning the chassis are how quickly and with
how much force the axle housing separates and drives the tires into
the starting line. Starting lines that are bald, slick, or extremely
hot will usually lack good traction. Therefore, a shock that has
had the extension (rebound) softened will create more traction (greater
separation). As the tire wraps up, the axle is driven down, and
the chassis pitch rotates, the sidewall of the tire is compressed.
At some point, the torque from the engine will decrease or the chassis
will reach maximum pitch rotation. When this occurs, the tires will
start to return to their original form perfectly round. This action
can cause wheel hop or can "unhook" the tire. Here is where the
compression setting becomes critical. The compression valving can
now be set stiffer to hold the tire down on the track. This method
of shock tuning is used by many of the most successful drag racers
in the sport today.
Currently the largest number of competitors in drag racing competes
in some form of E.T. (bracket) racing. The premise of bracket racing
is to predict the E.T. of the car as accurately as possible. The
race car must be setup with quality components that promote consistent
E.T.'s run after run. Common areas for tuning have included tire
pressures, new tires, and launch RPM. The link between the chassis
and the track is the shock/spring combination. A high quality suspension
system will load the tires evenly from run to run, thereby promoting
more consistent E.T.'s and allowing E.T. prediction to be more accurate.
More accurate E.T. prediction equals more round wins equals more
success and money.
AN INVESTMENT IN PERFORMANCE
The world of technology is ever changing, and in drag racing this is also true. A quick check of the competition will reveal that many have improved their programs, race cars, or teams. The goal is to better last year's performance or records. With that in mind, a constant evaluation of the combination is a must. From Pro Car to Competition, from Super Stock to Super Gas to Super Comp, from Super Street to a bracket car, a high quality set of shocks can and will improve the success ratio and will return its investment many times over. Drag shocks will last for several seasons. If the cost/value relationship is evaluated over time, the initial investment price can be justified by the opportunity for improvement that the shock provides. AFCO shocks will make a positive impact on your racing success!
AFCO Drag Racing Components are made up of racers who talk to racers,
chassis builders, and successful speed shops to stay on the leading
edge of technology. Technical support is always available, and an
ongoing research and development program is in place. Constant evaluation
and evolution are made possible through the use of our in-house
shock dynos and data acquisition equipment, and by attending races
and listening to the racer. We always welcome your input. The staff
at AFCO Drag Racing Components works for you, the drag racer.
THE WRAP UP
There are many combinations of race cars in use today. Through extensive
testing, AFCO has a vast library of shock/spring combinations. The
representatives at AFCO Drag Racing are an excellent source for
information and shock/spring applications. Custom valve shocks are
available and can be used to enhance the performance of a more extreme
or custom application.
An added feature to make the transition to AFCO easier is that we can dyno your existing shocks to baseline them. The technicians at AFCO can then adjust the shocks to closely match the setting from the original shocks. Guesswork on your part is removed. Our goal is your success. We want-and will work hard-for your support.