Why mount a shock upside down?
Two types of adjustable shocks
An Investment in Performance
Explanations 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 the suspension. 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 to shocks. 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 The majority of drag shocks being used today are old, outdated, and in need of rebuilding.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.
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?
TWO TYPES OF ADJUSTABLE SHOCKS
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.
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 are adjusted.
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.
AN INVESTMENT IN PERFORMANCE
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
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.