"SHOCK BASICS
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."
