Whether you’re racing, exploring trails or just having fun in the dirt, the right suspension setup makes all the difference to how your off-road vehicle performs. The experts at ADS Suspension know what it takes to get the right spring-and-damper combination, so we spoke with ADS director and former off-road racer and team manager, Bryan Grigsby, to get a handle on the most important terminology and concepts in off-road suspension design.
Let’s start with springs. The spring is there to support the weight of the vehicle. A common misconception is that a shock absorber will give you ride-height gain, but it won’t – it’s the spring that controls the static ride height. “The spring will always try to keep returning the vehicle to the static right height,” says Grigsby. “But if the spring is too stiff, the vehicle will never get into the suspension and let it do its job; too soft, and it will always try to blow through the suspension travel. With the spring there to support the weight of the vehicle, the shock can control the movement.”
It’s important to select the proper spring rate for the vehicle’s corner weights. ADS supplies a spring rate calculator to help with this process. Grigsby says that a good rule of thumb is to obtain the correct static ride height with 1-2 inches of spring preload on the shock. “Adding too much preload can result in ‘spring stack.’” he explains. “As you add that preload, the distance between the coils gets smaller and the spring will bottom out and become solid before the shock does. That will then transfer all the energy from the impact up into the mount and possibly break the mount.”
ADS exclusively uses Eibach springs, described by Grigsby as, “the finest springs on the market.” If you're looking to identify the length, rate and inside diameter of a particular spring, this information can be found embossed on the spring as a black part number in the format LLLL.DDD.RRRRC, where:
So, a spring marked 1400.300.0650S has a free length of 14 inches, an internal diameter of 3 inches, a rate of 650 lbs/in, and it’s colored silver. Simple!
Perhaps the biggest decision to make with off-road springs is, single-rate or dual-rate?
Dual-rate springs feature two different zones, each with its own coil spacing. They are a way of addressing the compromise between on-road comfort and off-road performance. On the road, the softer primary spring rate provides a plush primary ride – that’s comfort over longer, gentler undulations. But when you get into the dirt and need a stiffer rate to cope with shorter, sharper secondary ride inputs, the secondary rate will engage as the spring reaches that zone of its compression.
“Once you blow through the tender spring, which is what we call the primary rate, it enables that secondary rate to engage,” says Grigsby. “Then you have a stacked spring rate so it’s more linear and progressive. With a dual-rate you can use tuning to select where you want that rate switch to come in – based upon spring height, wire diameter, rate and preload.
“For our shocks in particular, we will choose a dual-rate spring whenever the length of the shock allows,” he continues. “Unfortunately, it’s very difficult to put a dual-rate spring on an OE-application front shock because it’s not long enough, so we’ll typically run a single in the front – unless it’s a long-travel application where we have the length for it. In the rear, where the shocks are a bit longer, our tuning has found that a dual-rate spring is the best setup for that application. Dual-rate springs are more expensive, but we want the customer to have the most optimized ride quality right out of the box.”
Dual-rates all-around are the norm in racing applications, where the front shocks might have a longer, 12- or 14-inch stroke. Customers typically contact ADS’s experts with their corner weights and receive recommendations for the spring rates they will need. All ADS shocks come with the hardware necessary to fit a dual-rate spring.
Dampers – also known as shock absorbers – slow down the forces in the suspension that are created by the vehicle going over different terrains. They do this by limiting the flow of hydraulic fluid through valving within the damper body. Different valve setups create different rates of damping, depending on the application and desired performance. “Damping force curves are matched to the spring rate for optimal performance,” Grigsby explains. “For example, if there isn’t enough rebound damping with too much spring rate, the suspension will ‘top out’ due to insufficient control in the valving. Too soft of a spring without enough compression damping will likewise blow through the available wheel travel. We often see improperly tuned shocks that have both: too stiff of a spring rate and not enough compression damping, so the vehicle is pogoing around because it’s overcoming the shock.
“It’s all about control. We’re using dampers to control the rate of compression and rebound so that the vehicle can come back to its natural ride height. If you’re driving through the desert and your vehicle maintains its ride height, that translates to less cab movement and less driver and vehicle fatigue. That also means smoother, faster progress because the tire spends more time in contact with the ground. It’s important to match the spring rates, shock length and valving. Everything must work together because the suspension is an ecosystem.”
ADS sells a range of shocks for different applications, with a range of options and services to match the range of expertise among the buyers.
Direct Fit products for example, which are an off-the-shelf OE replacement spring-and-damper combination, come preconfigured with damping curves that are matched to particular spring rates for optimal performance. Race shocks on the other hand, available with or without springs, are supplied with base valving for the customer to test and tune themselves, or by arrangement with specific tuning. If a customer buys a race package from ADS, its engineers will meet them in the desert to tune the shocks on the vehicle. The customer may also prefer to have them tuned by their regular aftermarket tuner.
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ADS manufactures several different styles of shock absorber/damper, including coilovers, bypass, internal bypass, and smooth body. With or without an external reservoir for the hydraulic fluid, most operate on the same principle of an internal floating piston that separates the hydraulic fluid from nitrogen gas. The rate of the damper is determined by allowing more fluid to bypass the piston, or less. A fluid restriction equates to a stiffer damping zone. But if more fluid can bypass the chamber, then it’s easier for the piston to travel through it, so there’s less damping effect.
The diagram below shows a cross-section of an ADS coilover shock with a remote reservoir. Further diagrams are available on the ADS website.
Our final step in this quick guide to off-road suspension concepts is to examine the differences between compression and rebound damping. In simple terms, compression damping controls the flow of hydraulic fluid through the piston to slow the shaft down on a compression event. Rebound damping does the opposite, controlling the energy of the spring as it wants to extend after compression – whether that’s a coil spring on the shock or a leaf spring on the vehicle.
As we’ve said already, it’s important to match the damping and spring rates together. The proper combination of compression damping and spring rate will keep the vehicle’s cab steady through rough terrain. Not enough compression damping will allow it to bottom out, which transfers the energy through the cab. Conversely, too much compression damping creates a very stiff ride so that again, the cab moves around too much.
“Rebound damping is at least as important as compression and has to work in concert with it,” Grigsby believes. “If you’re in a series of bumps or whoops, and your rebound damping isn’t proper, it won’t allow the shock to extend out fast enough to make the full length of available suspension travel available on the next compression event. This can lead to the rear ‘packing up,’ with the rear suspension travel reducing with each bump, until the point where there is not enough compression available to deal with the next one. That can ultimately cause the rear end of the vehicle to hit the bump hard, rear up and cause a very uncomfortable situation if you’re traveling at speed.”
All of ADS’s shocks are adjustable for both compression and rebound, some of them at multiple positions for extra-fine tuning. “With our coilover shocks for example, valve shims sit on the top and bottom of the piston for internal adjustment,” he explains. “Secondary external adjustment is done by a knob that has 20 positions of compression adjustment. Where our product differs from many competitors is that our compression adjuster bodies also have valve shims on them, so the knob itself can be tuned. It’s another way to control the flow and ultimately provide the customer with more control over the fluid circuits and damping.”
ADS’s most sophisticated shocks, the best-selling IBP MBRs, have seven zones of damping that can internally adjusted, covering both high- and low-speed damping for compression and rebound, and four channels of fine-tuning via external adjusters. “The IBP MBR does the jobs of both a coilover shock, which maintains the vehicle ride height and on-road comfort, and a bypass shock, which focuses on off-road performance,” says Grigsby. “When you have a vehicle that’s weight- or class-rule constrained to a single shock, or an application where it doesn’t make sense to have two huge dampers at each corner, we recommend the MBR.”
No matter what you're doing with your off-road vehicle, help is always just a phone call away – the folks at ADS Suspension are always happy assist in picking the exact combination of components you need to get the most out of your off-road vehicle. “You can pick up the phone and talk to somebody who’s extremely knowledgeable about the applications in which our products are being used,” Grigsby enthuses. “We love sharing our knowledge with customers, and we're proud that our shocks are completely built in the United States.
“We’ve been in the business for 30 years and draw on our racing heritage. The products we’ve developed stem from us finding the shortcomings of other companies’ offerings. We want to make sure that the consumer has the finest damper available, with safeguards built in to address anything that could possibly end your race or your day on the trail.”
Call ADS Suspension at 1-520-748-0005
