Shocks are both one of the most important aspects in a suspension and the most overlooked. Much attention is given to picking out just the right tubular control arms, and gearheads agonize over the decision between a three-link, four-link, panhard rod, Watt’s link, or whatever whizbang setup is the suspension du jour at the time. But when it comes time to pick out some shocks they often just fall back 10, punt, and hope for the best.
Part of this bad decision making stems from the buyer’s lack of understanding about what a key roll shocks and springs play in how their car rides and handles. In some cases manufacturers make it easier by packaging shocks with their suspension kits, but if not, it’s easy for someone to choose poorly rather than getting what’s needed to let the rest of their suspension operate at its full potential.
In a nutshell, shocks convert the kinetic energy of a spring’s movement into heat. With the energy converted to heat it can then be dissipated into the air through the body of the shock. Shocks and springs work together to maintain the maximum tire patch to the asphalt. If the road is flat and smooth this is pretty easy, but as corners and surface irregularities are added to the equation it becomes much trickier. If not for shock absorbers even the tiniest divot or bump in the road would send the car into an unending undulation down the road. This excessive bounce could be controlled by upping the stiffness of the spring, but that would result in a harsh and jarring ride that you would hate, but your dentist would love.
Fortunately, shocks do exist. While having the wrong shocks is better than having no shocks at all, the right ones can make a big difference in the performance of your Camaro and the quality of its ride. Nonetheless, in order to pick the right shocks it’s important to know a few basic concepts.
In shocks there are two basic settings: rebound and compression. Rebound damping helps control the part of the car’s sprung mass that is stored in a compressed spring and the rate determines how long it takes for the compressed spring to regain its static ride height. The farther you dial this up, the more the shock will resist the compressed spring’s effort to “rebound” to static height. Compression, also referred to as bump, is a damping function that controls the oscillation of the car’s unsprung weight. The higher the compression number, the more the spring will resist “compression” from its static ride height. Together these two forces work to give a car’s suspension its personality; either firm and sporty, or soft and cushy. Normally, compression is set less than damping, but like every rule, there are exceptions. One of these is when more compression is dialed into a particular corner to slow its downward movement, in essence giving the effect of a stiffer spring, however one should resist the urge to fix suspension issues through the shocks.
Also, spring rates play a role in this mix. They dictate how far a chassis pitches, rolls, or squats, while shock-rates determine how long it takes each of these movements to happen. But, that’s another story for another time.
Twin-tube Versus Mono-tube
For our purposes there are two basic types of shocks on the market today, twin-tube and mono-tube. Twin-tube shocks have been around for a long time. As the name states, the shocks are comprised of two chambers: an inner and a outer tube. The inner tube is where the piston moves through a main supply of oil. The outer chamber, or tube, contains an extra supply of oil and generally a low-pressure gas. This gas can be anything from regular air in the “el-cheapo” versions, to nitrogen in the nicer shocks. Whatever the gas, it’s typically pressurized at 100 to 150 psi. The downside is as the oil heats up, and it will under hard driving, it can mix with the gas and foam up causing shock-fade and a substantial dropin performance.
One key measurement that Steve Duck, of Race Car Dynamics (RCD), needs to know is how much room he has to work with. With the car at its ride height, a measurement is taken with the shock in the car from one eyelet to another. This data will help him determine what length shock will work best in a particular car.
The upside to twin-tube shocks is that they are inexpensive to manufacture and they provide a comfortable, stable, all-around ride. But they are not the best choice for performance—not by a long shot.
As you would guess, mono-tube shocks employ a single tube or cylinder. Even so, they typically have double the piston power compared to a twin-tube shock. At the end of the piston rod is the piston containing the valves. On compression, this piston pushes against a section of oil that is forced toward a second dividing piston. This second, or “floating,” piston is caught between this viscose oil and a pocket of high-pressure gas between 200 and 350 psi. Since the oil is separated from the gas, the chance of foaming is eliminated. This dual-piston single-tube design is the shock of choice when corner-carving performance is desired. In addition to mono-tube shocks being able to shed heat better than their twin-tube cousins, they can also be mounted inverted when required.
So which type is the right type for your ride? If you’re just building a cruiser and on a tight budget, then a set of twin-tubes will serve you fine. But, if you want to hit the twisties and squeeze out every bit of performance from your Camaro then mono-tube is the way to go. If you’re still skeptical, then take a stroll though the pits at any NASCAR, CART, IMSA, or even Formula 1 race and you’ll find that the only cars running twin-tubes are the spectator’s cars in the parking lot.
Steve Duck, of Race Car Dynamics, spends much of his time either advising customers on what shocks will work best under their car, or diagnosing pre-existing problems. As he told us, “Oftentimes, when choosing a shock, buyers are caught up in the hype of marketing. Just because a shock is billet-aluminum and has a knob on it doesn’t mean it will work on your vehicle, or that it is even a quality shock. When I’m asked how to set up a car, the first thing I always tell people is to set it up for how it’s going to be used. If the car is going to the track once or twice a year, they don’t need a race car. What they need to concentrate on is making it enjoyable the other 363 days. There is a distinct difference between a street car and race car. A street car with the correct shocks (like the Bilsteins offered by RCD), sway bars, and springs can still be a blast at the track without killing its street manners. On the other hand, a dedicated track or autocross car must be tuned for more control by using higher spring rates and shock valving that might have less low-speed bypass to react quicker in turns. Another big issue is guys who want to have their cars as low as possible. The negative of this is they end up taking away too much suspension travel, which kills the ride and the handling. Hey, at least they still have the killer stance!”
Dialing For Dampening
Another area of choice is in adjustability. Most higher-end shock brands offer both single- and double-adjustable shocks in addition to their standard-valved shocks. In a single-adjustable shock there’s one knob that changes shock-behavior. It’s a bit unfair to refer to some of these shocks as single adjustable since clicking the knob changes both the compression and rebound at the same time, while others just change one of these parameters.
As you may have guessed, a double adjustable has two knobs: one changes the compression while the other controls the rebound. This gives the ultimate in tuning ability. Nevertheless, this is only a good thing if you set them correctly. So, if you spend the extra coin, be sure to get some tuning advice from the shock’s manufacturer or you will be complaining about your ride when the fault is yours alone.
You could also go with a non-adjustable shock that has been custom-valved. The key here is to work with someone like Race Car Dynamics in order to figure out what valving would be optimal for your particular car and driving habits. We believe that if you’re going to go the non-adjustable route, then custom-valving is worth the extra coin, since it’s very hard to buy an off-the-shelf shock that is valved perfectly for your modified Camaro. One exception would be shocks that are included as part of a suspension package, or set up for a specific combination of parts.
Get What Works
When shopping for shocks, it’s critical to get the right parts for your particular ride. We asked 11-time autocross champion, Mary Pozzi to give us her thoughts on this issue. “It’s pretty basic really,” says Mary. “Ninety-eight percent of drivers haven't a clue if a shock's working properly, or at all for that matter. I mean, how many times are you driving along at freeway speeds all the while watching a wheel and tire on the car ahead bouncing up and down? What you're seeing is a shock that is most likely blown on rebound underneath a completely oblivious driver. When I was selling auto parts, we'd have customers come in and see a set of shocks laying on the counter. Immediately, they'd grab a shock, tug it apart, and push it back together trying to imitate their car going over a speed bump. They would then pronounce it fit for automotive use or cast it aside like a rotten pear. I'd laugh, but not too loudly as I did want to sell parts. It's impossible to manually reproduce cyclic compression and the release of an automotive suspension system without a shock dyno. Quality matters. So don't be tempted to purchase a shock by price. Proper shock selection is vital for your Camaro.”
Valve design is key to how any shock functions because it controls the flow of oil from one chamber to the other. When the piston pushes down into the shock the oil is forced through the valve. Since only a small amount of fluid can pass through the valve, hydraulic pressure is created, which dampens the spring’s energy. Most shocks today have dual-purpose valves. When the road is smooth, the valves open more for a softer ride, but when the action picks up, the valves close off for extra stiffness.
The Inside Story
On the left you can see the two parts of a mono-tube shock, while on the right the three main parts of a twin-tube version. Most notable is how much larger the mono-tube’s piston is compared to the twin-tube’s, even though the shock bodies are almost the same size. Bilstein's larger piston and deflective-disc valving develops controled force when needed at the slightest movement of the suspension. This results in weight transfer when you need it. This means better control under braking, and your tires will stay glued to the road even through the rough spots. Bilstein's patented deflective disc valving system allows for exact valving of both compression and rebound movements.