The evolution of Pro Touring is an interesting one. It's gone from thinly disguised race cars that only young guys with healthy backs could endure on the street, to mega-dollar show cars that log most of their mileage driving up and down trailer ramps. However, in an interesting and somewhat unexpected turn of events, the most recent crop of six-figure Pro Touring machines have proven themselves on the track in ways no one could have imagined just a few years ago. Thanks to events like the Optima Ultimate Street Car Invitational and the American Street Car Series, these high-profile street machines have earned the respect of the staunchest of naysayers while smoking Corvettes and Porsches along the way. Playing in this arena requires some serious suspension hardware, and that's right up the Roadster Shop's (RS) alley. While the suburban Chicago-based shop may be best known for their ultra high-end, award-winning muscle car builds, it has been manufacturing complete chassis and cutting-edge suspension hardware since day one. To get a better understanding of how factors such as suspension pickup points, spring location, camber curves, bushing design, and sway bar stiffness affect ride and handling, we had Jeremy Gerber explain the technical elements of design that go into all of the Roadster Shop's suspension components.
There are many shortcomings of a factory muscle car suspension design, and perhaps the most significant is the location of the suspension pickup points. It is easy to correct factors like floppy bushings and weak hardware by simply upgrading to a bolt-on aftermarket control arm. What you cannot achieve is the relocation of the suspension pivot points or changing the geometry of how it functions. When your average enthusiast looks at a double wishbone suspension, they oftentimes see no more than a pair of spindles attached to some control arms with a set of coilover shocks providing the motion control. The majority of people see the control arm pivots as a simple means of attachment that have no purpose beyond connecting the control arms to the spindle. In reality, the location of these pivot points are the core and most important feature determining the performance of your front suspension. On the RS Fast Track suspension, there are countless hours of engineering and design time invested in simply locating the control arm pivot points in order to yield the best possible performance in the industry. In a computerized 3-D suspension model, we are able to plot the location of the roll center and instant center of the suspension system and optimize its location and manipulate ride and handling characteristics. The pivot points are more than just mounting locations. They form an invisible grid in the suspension design software that allows mapping the swing arm lengths of the control arms, antidive percentages, caster and camber gains, and a variety of other performance factors that ultimately contribute to designing a high-performance suspension system.
Ride and Handling Balance
A hallmark of running an aftermarket front clip or frame is having an outstanding balance of ride quality and handling. There are many clear and simple advantages of utilizing a complete aftermarket chassis, such as added strength, rigidity, and ride height. While these key items are very straightforward and easily identifiable to the customer, what cannot be shown in an advertisement is the ride quality, feel, and performance of the chassis. In order to obtain this, we have found that beyond our in-depth engineering of suspension components there is a lot of knowledge to be gained from building, testing, and tuning vehicles. We go to great lengths to design a complete package where the rear suspension works together well with the front suspension, making the car perform great as a complete package. Many overlooked items, such as exhaust routing, crossmember locations, and body mount locations lend themselves to the ride quality of a car. It is very important to make sure that no moving or vibrating parts come in contact with the body of the car in an effort to eliminate interior vibrations. The springs and coilover shocks lay a massive roll in the ride quality of the car. In order to use them to the best of their abilities, however, we have optimized the motion ratios of our front and rear suspension packages to allow the use of lighter spring rates for a smoother ride while not sacrificing performance. Simply put, where some suspension systems require the use of a 600-lb/in spring to hold your vehicle up to its ride height, a Roadster Shop chassis may only use a 450-lb/in spring. We do not rely on high spring rates for roll resistance through cornering, and instead we have designed a system that lets light springs provide great ride quality while utilizing splined sway bars to keep the roll angle of a car to a minimum.
Muscle cars are by no means lightweight machines, and the stress on the chassis is compounded by today's modern tire compounds and massive horsepower output. Consequently, all RS framerails are built from 10-gauge mild steel, providing a super-solid structure for the rest of the chassis. In addition to this, we integrate a variety of 0.250-inch plate steel gussets and 0.125-inch wall tube crossmembers to make our chassis as rigid as possible. There is a huge difference between a dedicated race vehicle and a muscle car you intend to drive on the street, and strength in the suspension components is one of the key differences. We sacrifice nothing to provide the strongest control arms and suspension components possible. Our lower control arms are built from 1.625-inch tubing with 0.125-inch wall thickness, which is more than twice the diameter and strength of other systems on the market. Our upper control arms are built from the same material, only in a 1.25-inch diameter. We use 4130 chromoly, pre-hardened upper control arm shafts that can withstand any abuse the road or track can throw at them. Heavy-duty machined components are utilized all throughout the suspension to make sure that no pothole or imperfection in the road will cause harm to your suspension. Years ago, a 500hp big-block Chevy was considered a high-performance street motor whereas today it isn't uncommon to see 850-plus horsepower LS motors that are lighter and more efficient. When you factor in the effects of wider and stickier performance tires, it is crucial that a suspension system and chassis be up to par. We cut no corners when it comes to strength and materials. We do not use commonly available components that may fit the bill. All components have been designed and built specifically for our application. By doing this, RS suspension components can handle in excess of 1,500 hp. With built CV axles utilizing chromoly CV joints and 300M axleshafts, even our independent rear suspension units are able to accommodate these massive horsepower demands.