Racing Shock Absorbers - Shocks 101
By Removing Some Of The Mystery Around Shock Absorbers, You Can Understand The Role They Play In Making Your Car Faster, Safer, And Easier To Tune
From the February, 2009 issue of Stock Car Racing
By John Hill
In the view of some racers, shock technology is shrouded in mystery.
Part One of Two: Shock absorbers will elicit an emotional response from any racer. Yet, this is a part of the suspension that is shrouded in mystery. That's true not because shock absorbers are a complex part, but because not everybody is free with information on the operation and tuning of shocks. Racers are at times a tight-lipped lot. Knowledge that equates to a winning setup is an advantage, and you do not want to give your competition any advantages.
It is easy to look at a spring and understand what it does, no matter if it is a coil spring, a torsion bar, or a leaf spring. Visually, it is very easy to understand how it works and the role it plays in the suspension. The same can be said for A-arms, spindles, and axles. It is easy to understand the roles these parts play in the suspension's operation.
This type of shock is adjustable from the cockpit.
Shock absorbers, though, are somewhat of an unknown. The biggest driver of the mystery is that many racers do not really understand the role that shock absorbers play in how the car feels to the driver, how the car responds to changes in tires and springs, and ultimately, how the car as a whole responds to the track.
From a simplistic view, all the shock absorber has to do is keep the tire in contact with the ground as the suspension articulates. The shock absorber converts the up-and-down motion (kinetic energy) of the suspension into heat, which is transferred into the shock through oil that is forced through orifices or valves in the shock. This causes the shock to dampen or control the movement of the suspension.
Without shocks, the springs would keep oscillating until the wheel movement caused by a bump in the road dissipated or until the car was stuffed into the wall. With a set of shocks we can control the bounce or oscillation and keep the wheel and tire combination planted on the road as the car travels over the track. We can adjust the shock to suit a specific condition or make the car behave in a way that we deem desirable.
The driver can make changes to the rebound while the car is on the track.
So, why are shocks such a mystery? First, the vocabulary surrounding them is often misunderstood. Let's look at definitions of terms used to describe the shock and its activity.
Dive: A pitching motion, usually in reference to deceleration. The sprung mass of the vehicle moves forward, the front of the car compresses the springs, and the rear of the vehicle extends the springs. As the car slows under braking, it dives forward. This places the front shocks into compression and the rear shocks into a rebound condition.
Squat: A pitching motion, usually in reference to acceleration. The sprung mass of the vehicle moves rearward, the front of the car extends the springs, and the rear of the vehicle compresses the springs. This places the front shocks into a rebound condition and the rear shocks into compression.
The rebound adjustment is easily accessed on the QA1 shock absorber. This allows the crew to adjust the rebound settings without disassembling the shock or removing it from the car. Photo courtesy of QA1
Compression: The act of compressing the shock. The shaft moves into the body of the shock. During compression, the shock becomes shorter and the wheel travels in an upward motion.
Rebound: The shock extends and the wheel travels downward during the rebound stroke.
Dive and squat are attitudes that the car assumes as it accelerates or decelerates during any given lap. The adjustability or tunability of the shock absorber enables the racer to make the car adapt to changing traction conditions. The setup utilized with the shock absorbers determines how the racer adjusts dive and squat. Yes, other suspension parts play a role in dive and squat-such as antiroll or sway bars-but the shocks are the major players in the attitude the car attains as it travels around the track. The attitude the car assumes in any given condition is directly influenced by the settings that affect the compression, rebound, and valving of the shock absorbers.
Twin Tube: Just as the name implies, there are two tubes used in the design of the hydraulic portion of the shock. This shock utilizes an inner and outer tube and is usually found in OEM applications. The inner tube houses the piston and is commonly referred to as the pressure tube. The outer tube is used to store fluid, and in some applications the outer tube can be pressurized with a gas, usually nitrogen.
This shock is mounted behind the rear end in a vertical position. This position is preferred because some shocks gradually lose effectiveness as the angle becomes less vertical. It is a good idea to check with the manufacturer to get recommendations for mounting.
Mono Tube: This design uses only one tube, and some designs use two pistons. The majority of racing shocks utilize this design.
Many of today's crew chiefs in the top levels of our sport play serious games with shock absorbers. At superspeedways such as Daytona and Talladega, they manipulate the shocks and effectively turn them into hydraulic struts. The shocks become tools to help change the attitude of the car. For example, the front shocks are adjusted and calibrated in such a way that the rebound is basically non-existent and the shocks compress as the car goes over bumps or enters a corner, and they remain compressed. While this may not work for race conditions, it makes the car faster for one or two laps of qualifying. This activity has sent more than one or two crew chiefs to the penalty box. Shocks are a very special tool to be used in your tuning arsenal.
In the world of the Saturday night racer, it is important to develop a shock that is durable, tunable, and affordable. Many weekly racers do not fully use all of the adjustability that the modern racing shock has to offer; subsequently, they are not developing a package that gives them all the shock has to offer. With that in mind, here is a list of questions and answers that may help the weekly racer become better informed when it comes to shock usage and selection.
What is the biggest error that the Saturday night racer makes in regard to shocks? Racers make the mistake of assuming that all shocks are the same. Different shocks affect the race car's performance in various ways. One shock setup will allow the car to enter or exit a corner better than another shock. Racesr have to experiment with the compression and rebound characteristics, possibly even delving into the shock to change the valving. This last step may require purchasing some additional parts, and most of the manufacturers we spoke with have alternate valving available.
Why is a racing shock better than a heavy-duty OEM shock? Racing shocks have tighter tolerances than OEM shocks. The valving is quite different from a shock designed for a truck or a performance-type car. The speed range in a racing shock is different from that of an OEM shock. In this instance, speed is the velocity at which the shock operates. Also, racing shocks offer more tunability than OEM shock
Shocks live in a very hostile environment. Notice the dent in this twin-tube shock's body. One advantage the twin-tube design has over the mono-tube design is it takes more abuse while continuing to work. If this dent was on a mono-tube shock, it would be rendered inoperative.
Does the racer have to purchase rebuildable shocks to get good performance? No. There are many non-rebuildable shocks on the market that give the racer good external adjustability through external compression and rebound adjustments. These adjustments work, but the range of adjustments may be a bit limited. To take the next step, the rebuildable shock offers more options. It may even save some money because it doesn't require the racer to buy as many different shocks.
If a racing shock is used, how many different shocks are necessary? This is a question that can be answered in two words: it depends. It is not uncommon for a racer to travel with many different types and brands of shocks so they can adjust around the conditions the track may present on any given occasion. This is true even if the racer races at only one track. Even if the shock is rebuildable and revalveable, the racer may require multiple shocks, as time is often a factor. It may not be practical to revalve a shock during practice, although some of the shocks can be disassembled and reassembled in as little as 10 minutes. One factor in the racer's favor is that many of today's racing shocks are adjustable from the outside. Also, many shocks have provisions for adjustments to be made by the driver while the car is on the track.
Is there an advantage in using a coilover shock versus a non-coilover? If this type of shock is legal at your track, a coilover has some advantages. But coilovers are limited to the physical advantages of using a smaller spring. This allows racers to have finer selections on the springs from a rate perspective, but the shock's performance is really no different. A well-designed race shock is a well-designed race shock.
Does the racer using a street tire put different demands on the shock than someone using a racing tire? No. The demands and requirements of the shock are the same. Control the suspension and keep the tire in contact with the track.
What about dirt versus pavement? Are the demands placed on the shock different enough to require a different shock? Yes, the demands are different but not so different that the shock can't be adjusted to compensate. Shocks used on pavement cars tend to require a greater level of low-speed dampening, and shocks that are used on dirt cars require less. Pavement shocks are usually set up with stiffer valving, which may result in a greater level of heat and can cause the oil to degrade at a more accelerated rate than the dirt shock.
This racer is tuning the car by adjusting the air pressure in the shock-just one more tool to affect how the car "sees" the track.
It is clear that there is a wealth of knowledge within the racing community in regard to shocks. The trick is knowing who to ask for the information you need. All of the manufacturers we contacted were more than helpful. Most of them have employees who communicate and disseminate information about shocks full-time.
I wish to thank those who were instrumental in filling in some of the blanks regarding the hows and whys of shocks. The folks at AFCO were very helpful. Christine King and Mark Bauer at QA1 went above and beyond answering questions and providing materials. With the kind of support that these manufacturers were willing to give, you can be sure they would be just as helpful to the racers who are using their products.
The next installment will focus on how racers can adjust the shock and/or compensate for specific track conditions. This is intended to help the racer understand how compression, rebound, and valving affect the car, and ultimately, the car's performance.
It is our desire to remove some of the mystery around the use of the shock and the role it plays in making your car faster, safer, and easier to tune. Racers should not be afraid to make changes and try to improve the car. The shock is not that complex once you understand how it works and how it is assembled. The shock, in fact, should be your new best friend.