Dec 2, 2009

It’s all about relationships in the world of suspension. Broken down to individual pieces, the internal components of any aftermarket shock available today don’t seem like much; but how they interact with each other to produce the results that drivers want is both simple and extremely complex.

Upgrading a customer’s suspension may make a greater difference in their driving enjoyment or their lap times than any engine upgrade.

“You can take three-tenths off of your lap times just by changing a shock on the left of the car; an engine builder can’t give you that. Everything’s in the timing; what we do is watch and tune. It’s a very simplistic way of gaining control. Drivers can make their own changes or rely on me to make the changes that I think will help, then I tell them why I think that would help, and they can tune it from there,” says Bob McDowell, technical director for AFCO Racing Shocks.

“Depending on their budget, they might do just the front first or the back first, but it’s like being a drug addict; they will keep coming back for another hit,” says Pete Basica, Pedders USA, West Olive, Mich.

Whether the shocks you’re selling are adjustable or not, gas-charged or not, have an external reservoir or are a mono- or twin-tube, the fundamentals are very similar.

The Function

If you pare it down to the basics, shocks are pretty simple. The trouble is that their name is misleading regarding their actual function. Despite the fact they’re called “shock absorbers,” they actually act to support the spring.

“We generally refer to shocks and struts as dampers, because the function of a hydraulic unit is to slow or control the rate at which the spring responds. Most people refer to that the same as a shock absorber, but that’s wrong. The shock on vehicle is actually the spring,” says Basica.

When a car or truck hits a bump or drops into a hole, it’s the spring that responds, and the shock that keeps that response in check by slowing the compression (upward) or rebound (downward) stroke.

“The shock is there to control the spring. The larger the spring, the more force you need to control it,” says John Marking, vice president of off-road suspension, Fox Racing Shox, Watsonville, Calif. He adds that when built correctly, the shock should control the spring; you don’t want the spring to overpower the shock.

The Oil

The oil inside the shock body is the media that allows the shock to function. The oil’s viscosity slows down the shock’s movement as it flows through the piston. As a result of that force, shock oil can build up quite an amount of heat.

“The most important factor for high performance shock oil is temperature stability. This is measured by the viscosity index. We try to stick with a V.I. of 380 or better. Our best oil will function from -60°F to 400°F,” says Marking.

Nitrogen acts to keep the oil in its functional state. Under heavy use, oil can cavitate, or foam or froth. When that happens, the shock loses its main ability to control damping.

“When you run too low of gas pressure in a shock, it places greater force on the piston, and turns the oil into foam or vapor. That gives your shock a big delay or dead spot. You need to have enough pressure on the opposite side of piston to avoid cavitation,” says Adam Hornburger of Penske Racing Shocks, Reading, Pa.

The nitrogen, compressed to anywhere between 100 and 250 psi inside the shock, provides that pressure.

“Keeping the oil under pressure with nitrogen is like putting a radiator cap on a vehicle. It lowers the point at which oil would foam. Nitrogen keeps the unit more stable,” says Basica.

The Adjustment

Externally adjustable shocks come in a range of options. Some feature only one rebound or compression adjustment, while others may offer drivers the ability to dial in both high- and low-speed compression or rebound settings. This increased driver adjustability is a response to demand from drivers, especially those who may want a daily driver they can race.

“The technology is advancing at a rapid rate; enthusiasts would want to drive more from their suspension setups than in the past. This is something enthusiasts are looking for these days; they are going to the drag strip or race track, and while it’s not so much that they require damping adjustment, but they want that upgraded knowledge and want to push the envelope further. You have to address each one (rebound and compression) independent of each other so you can choose how you want your car to behave,” says George Ciordas, marketing manager, KW automotive North America, Inc., Sanger, Calif.

The Piston and Shims

The piston is the workhorse of the shock. Located in the main bore of the shock, the piston is a somewhat hockey-puck-shaped device with ports for oil flow on both the compression and the rebound side. The shim stacks are located on either side. In nitrogen-charged shocks, a floating piston rides between the oil and the nitrogen charge.

As the oil flows from one side of the shock to the other through the ports on the piston, it passes shims-thin, washer-shaped discs of flexible metal. The shims deflect under the force of the oil’s pressure, and the rate at which they deflect affects the oil’s movement and thus the suspension’s response. Different sizes and thicknesses of shims determines at what point they deflect to allow the oil to pass through, and that allows fine-tuned control, or valving, over the movement of oil through the shock.

“Shims and piston design come into play, coupled together for control. We built a shock curve, starting with the basics. From there begins the manipulation process. Somewhere, throughout this process, each company picks what speed they run the shock at to quantify their valving code. There’s not really a motorsports industry standard. It’s a secret of how you build control into a shock to be competitive.”

Shocks come from the manufacturer valved for a specific vehicle and driving conditions. But, drivers with more exacting needs may elect to revalve their shocks themselves, in order to gain more or less compression or rebound damping above and beyond what external adjusters allow.

“You can really optimize settings for better launch control. It’s a driver-feel thing; most drivers are very knowledgeable, but don’t give themselves as much credit as they should. The valving is our job here to make sure it’s as close as possible. If they are making their own adjustments, they can easily give us a phone call, and we can help them through it,” says Hornburger.

The Externals

The body and shaft of a shock are the parts most visible, but simplest in function. While conditions demanding extreme loads on the shock may require shocks with a larger body and shaft, most shocks have a 2-inch diameter body and 5/8-inch shaft. For shocks with an external reservoir, the reservoir acts to hold the displaced nitrogen gas during the compression stroke of the shock.

“Shafts come in 7/8-inch, 1-inch, 1 1/8-inch and1 1/4 inch. It’s all about the strength of the unit. If you’re going to generate greater force, then use that to figure out what shaft you’re going to use. It’s a function of weight and of how the thing’s going to be used. I’m just coming back from a short-course race last weekend. It’s pretty violent; the trucks run into each other occasionally, and we need to take that into consideration.”

Supporting Actors

Suspension geometry is more complicated than just the shock, of course. Components like sway bars and bushings play a huge factor in a properly tuned suspension.

“The rubber bushings are used as part of the suspension. When the wheel goes into a depression and falls downward, the rubber is put under a load, and it wants to spring back to its at-rest position. When the wheel is compressed upward, the bushing wants to pull it back down. It’s almost like second set of springs. When we do suspension, we take into account how the rubber bushings function in vehicles,” says Basica.

Not all bushings are rubber, either. Drivers have a choice of rubber or urethane, each with different properties, according to Brian Skipper, president, Sway A Way Inc., Chatsworth, Calif.

“It depends on the amount of performance they’re looking for, and what they’re trading off. You get better suspension geometry using urethane bushings, but they transfer more noise to the vehicle. Under hard cornering forces, rubber will comply a lot more, and the suspension will move; the camber, caster and toe-in are no longer where they’re supposed to be. Urethane will hold it where it was intended to be. With rubber components under high cornering forces, the geometry may change 1-2 degrees,” Skipper says.

The Sale

It all boils down to making the sale. In order to have a happy customer-who may come back for more-making the right sale is more important than making the biggest sale.

“The customer needs to understand if they want a performance feel or a street/stock feel to their car. It gets down to how they’re going to use the vehicle. If it’s a daily driver, recommend softer settings. If they’re going to go drive the car hard and want it to corner well, they should go to firmer settings,” says Skipper.

Suspension makers agree that most customers estimate their needs to be more aggressive than they really are.

“You have to get past the ego. There is always going to be people who have to have all the bells and whistles, even if they never use it. But if that’s what they want, then that’s what they want,” says Ciordas.

A customer who hits the local drag strip twice a year or takes a 4×4 to the ORV park once a month has different needs from the competitor with a dedicated race vehicle. Yet many in the first category like the idea of having a full, race-tuned suspension setup, even if they won’t need the full range of control or tuning ability it gives them.

“The key in the aftermarket is to make sure that what we’re hooking a client up with is not only applicable to their driving style but it’s what they really want. If you talk to a guy, and he understands all that but still wants rock hard suspension, because once a year he might go to a track day, then selling him rock hard suspension is the right thing to do because he made an educated choice. But bolting on too hard or too soft suspension because we like it is where we go wrong as an industry,” says Basica.