Roadster Shop Suspension Components Explained - How It Works

Roadster Shop gives us the down and dirty scoop on the most fundamental and the most advanced of suspension design concepts.

Stephen Kim Jun 3, 2013 0 Comment(s)

Spindles and Camber Gain

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Spindles play an important role in overall suspension design, and the C6 Corvette spindle is an outstanding foundation to build a performance muscle car suspension off of. They are a very high strength and lightweight design, and offer a nice, tall ball joint that allows for great camber curves to be built into the suspension. When raising the location of the upper ball joint on a spindle in relation to the lower ball joint location, you are now given a larger window to raise and lower your upper control arm pivot points, thus increasing or decreasing the camber curves. When set up properly, you can achieve some pretty fantastic camber curves that are an improvement even over the stock Vette geometry. The taller design limits you to a minimum of a 17-inch wheel diameter, but provides a good sturdy base with its height that resists the massive twisting forces that are transferred through them during hard braking. Another key advantage is that there are countless aftermarket and OEM performance brake packages available as a bolt-on for the stock C6 spindle. This spindle design utilizes a bolt-in sealed bearing hub that is available in stock form as well as upgraded units designed to withstand the abuse of road racing and autocrossing.

Dropped Steering Arm

While the C6 spindle has many great features, the one downside to it is the stock steering arm location. The Corvette is set up with the crank pulley of the motor behind the steering rack so the height of the steering rack is not a factor. However, when retrofitting the C6 spindle into a muscle car, the engine's oil pan is now directly above the steering rack, causing a conflict and a massive packaging issue. The solution is our billet aluminum dropped steering arm. It lowers the mounting location of the steering rack and tie rod considerably while still retaining the best steering geometry and Ackerman possible. As a result of this, we are able to mount the steering rack low in the chassis and accommodate most any engine package.”

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Splined Sway Bars

Splined sway bars have been used in racing for many years and have recently been adapted into Pro Touring cars. They offer many strength and versatility advantages over a traditional sway bar. More specifically, splined bars are available in a variety of wall thicknesses and diameters to provide different levels of roll stiffness for different applications. We have a very solid baseline for what bars work the best for muscle cars, but for the more serious driver it is nice to be able to fine-tune the car with the use of different wall thickness sway bars. In addition, we utilize a broached sway bar arm that can be cut to any length and made adjustable to provide infinite tuning possibilities for the roll stiffness of your car. Many suspension systems simply use mild steel DOM tubing for a sway bar that really provides no roll resistance. Since they are not sprung steel, they can fatigue very easily.

Trick Bumpstops

Roadster Shop utilizes jounce bumpers on our front and rear suspension systems to limit the suspension travel during compression. This prevents the shock from absorbing the force of heavy impacts on the road. By doing so, it increases the life and performance of a coilover shock. If a suspension system does not have a jounce bumper, it is relying on the shock to take the impact of road obstacles like potholes and large dips, which can severely damage your coilovers and even cause shock mounts and other components to shear off during impact. Aside from the protection it provides to a coilover, a jounce bumper also offers performance gains since they work as additional spring rate when the suspension begins to fully compress. The RS Fast Track suspension also integrates an upper bumper that limits the extension of the suspension travel. This aids in the assembly process and allows us to bring the coilover shock outboard as close to the ball joint as possible. This enables orienting the shock as vertical as possible while preventing the upper control arm from contacting it. In contrast, many suspension systems make sacrifices in this area and resort to mounting shocks at unacceptable angles.

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Bushing Materials

A lot of research and testing has gone into the bushings that we use in our Fast Track suspension. We have chosen a combination of a bronze Oilite sleeve and an Acetyl bushing, which we feel is the best possible design for a vehicle that will be both street and performance driven. The Acetyl bushing provides almost no deflection while still providing a barrier from road feel and vibrations. It is a much better solution to using Heim joints, which can be noisy and often wear out quickly. Rubber bushings can provide a nice ride, but will deflect heavily under cornering loads and drastically inhibit the performance of your suspension. Over the years, we have seen mostly negative results with the use of urethane bushings. Not only are they noisy, but they still deflect very easily. Unless they are properly designed and have supporting washers, they are prone to wearing our rather quickly and deforming under normal driving conditions.

Maximizing Tire Clearance

Fitting massive front tires is the norm these days in Pro Touring machines. Most Pro Touring cars compete and drive with street compound tires, and as competition gets more and more intense so does the need for more traction. Going to larger front tires is a natural fit when looking to achieve more bite without using a softer compound tire. In order to package these larger tires, we have specifically designed our upper and lower control arms to avoid any interference when moving through their steering motion. A swept-back lower control arm can accommodate front wheel backspacing up to 8 inches while still retaining greater steering angles than most stock and aftermarket suspension systems.

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IRS Advantage

The solid axle four-link rear suspension is probably the most common rear suspension seen on muscle cars, street rods, and Pro Touring cars because of its ease of packaging and relatively good performance. It has been proven over the years that, when set up properly, it can work quite well. However, simply put it cannot match the performance advantages of an independent rear suspension setup. If you look at modern cars, the only thing on the road with a solid rear axle is a pickup truck. For the diehard drag racer, a parallel four-link solid axle will always be the best performing option, but for the Pro Touring and cruising enthusiast there are some significant advantages to be had with our IRS. For general driving and cruising on roadways, the ride quality will be a huge advantage, as the IRS can absorb uneven surfaces and bumps by allowing the wheels to move independently. This allows the tires to do a better job of dampening and maintaining traction. This advantage is even amplified in racing applications where dropping a tire off track or putting one tire on the rumble strip can really upset a solid axle car. With an IRS setup, the car will maintain traction and control while allowing one wheel to absorb the obstruction.

Furthermore, an IRS allows precisely controlling the camber of the rear tires. We have built-in camber curves that match well with our front suspension, creating a very predictable and great-feeling total package. Close attention has been paid to the balance of roll center height and sway bar rate in order to optimize traction and handling of a vehicle on street compound tires. Heavy muscle cars with street tires require a substantial amount of weight transfer during cornering. This allows loading the rear tires sufficiently to make them stick to their maximum potential without causing a car to understeer. A 1.25-inch splined rear sway bar has been integrated into our IRS cradle and can be easily swapped for lighter or heavier bars to fine-tune your car's performance.


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