Muscle Car Suspension Basics - Turning The Corner

If You Want To Maximize Handling, You Have To Understand The Basics Of Suspension Design And Spend Money Where It Counts Most

Stephen Kim Sep 1, 2009 0 Comment(s)
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Although air suspension systems trace their roots back to show cars, Air Ride Technologies has proven that air suspensions can more than hold their own on a road course. Air is an excellent springing medium; it gets stiffer the more that it's compressed. Likewise, it can also be set up to behave in a very linear fashion. Unlike traditional coilovers, an air suspension can be adjusted at the touch of a button. These trick Shockwave units feature integrated double-adjustable shocks.

Removing the "core" from the middle of a sway bar may suggest a significant decrease in stiffness, but that isn't the case. "Depending on wall thickness, a hollow sway bar can be just as stiff as a solid bar for any given diameter," explains Chris Alston of Chassisworks. "The big benefit is that a hollow bar is roughly 30 percent lighter. Additionally, during the design phase we can easily make changes to the sway bar's overall stiffness by altering the wall thickness of the tubing. Another advantage is that a hollow sway bar tends to 'unwind' faster than a solid bar after it has been twisted."

Bearing the brunt of suspension loads, springs can take the form of coils, leaves, torsion bars, or air bags. A spring's most important job is supporting the weight of the chassis, but it must also allow the tires to follow the contours of the road while providing roll stiffness in the corners. Consequently, optimizing one aspect of spring performance often compromises another, which we'll discuss later in this story.

Perhaps the most important aspect of spring design is its spring rate, which is different from spring load. Spring rate is simply how much force it takes to compress a spring one inch. For instance, a 200-lb/in coil spring requires 200 pounds of force to compress 1 inch. Spring load, on the other hand, is how much weight a spring can support at a given height. While spring rate does not change as a spring compresses, spring load is reduced. In other words, the farther a spring is compressed, the less load it can support. This is why a shorter spring must have a stiffer rate than a taller spring in order to support the same weight.

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Shocks damp spring motion by converting kinetic energy into thermal energy. Under rigorous use, a shock will begin to fade and lose its damping ability if it can't dissipate heat quickly enough. To combat this effect, DSE has designed an optional remote-mount reservoir canisters that reduce shock fade by increasing fluid capacity.

Most production cars and race cars utilize linear-rate springs. However, some aftermarket springs have a progressive rate, which means that they get stiffer the more they compress. The logic behind this design is to initially provide a softer rate to help absorb road irregularities, then stiffen up the more it's compressed to limit body roll. The true effectiveness of progressive-rate springs is debatable, but they have amassed legions of followers nonetheless. "When matched with the right shocks, a linear-rate spring can ride and handle better than a variable-rate spring," says Kyle Tucker of DSE. "With a variable rate spring, the shock valving must account for a wide range of spring rates, which can adversely affect ride quality and handling. A progressive spring rate is just another variable to account for when fine-tuning a suspension."

The term shock is the biggest misnomer of any suspension component in existence. Everywhere else in the world, shocks are called spring dampers, which precisely conveys their job description. "Without shocks, springs would just gyrate until the friction from the bushings slowed them down," Chris Alston explains. "Springs simply hold up the weight of the car and absorb suspension loads. By damping the motion of the spring, shocks determine the rate of weight transfer, and optimizing weight transfer is what good handling is all about. The shocks essentially control how the suspension operates, and you can't achieve the ideal valving for your combo without an adjustable shock. I'd venture to say that as long as you have a good set of tires, the shocks are the single most important components of the entire suspension."

Double-adjustable shocks allow independent damping of both compression and rebound. Some single-adjustable shocks change the damping of the compression or rebound, but not both, while others change the compression and rebound valving at the same time in equal amounts. Some adjustability is better than none at all, but double-adjustable shocks allow on-the-fly fine tuning that single-adjustable shocks can't match. "Since you don't have time to swap out sway bars at a road course, the easiest way to dial in a suspension is with the shocks, and you really need the ability to adjust compression and rebound damping independently to do it right," explains Kyle Tucker.




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