Autocross Wheel Basics with Forgeline: Picking the Right Rollers
Modern muscle car enthusiasts are more likely than ever to test their machines at the race track. And we’re not just talking about going fast in the quarter mile; today’s enthusiasts are building cars that not only make serious horsepower but also handle like true world-class sports cars. As a result, these cars and their owners are suddenly finding themselves right at home on autocross courses, all around the world.
Autocross, also known as “auto slalom”, “Solo”, or “Solo 2″ racing, is a competitive time-trial that is typically hosted in large parking lots on tracks comprised of orange traffic cones. Popular with most sanctioning organizations including SCCA, NASA, and others, these relatively short courses with tight corners are less likely to test maximum speed and more likely to test a vehicle’s handling limits and a driver’s skill and smoothness. And because participants are racing at slower speeds against the clock with few obstacles (as opposed to the mayhem of wheel-to-wheel and door-to-door road racing), the potential for serious damage is minimal, making it a great sport for almost anyone who loves to drive.
But even though autocross is friendly to beginners, it is also a serious sport that offers a wide range of vehicle classification (depending on preparation level) and an abundance of intense competition. And like any competitive environment, enthusiasts are always going to push the limits of performance. So we wondered, as the speeds get faster and the cornering loads get higher, what are the implications for our wheels? Is just any wheel safe for exploring the cornering limit? And when we’re ready to invest in a set of performance wheels to improve our capability on the autocross course, then what exactly should we be looking for?
We posed these questions to David Schardt, the owner of Forgeline Motorsports, makers of some of the finest custom and performance wheels on the market today. Dave is not only an expert on wheels, but also a lifelong motorsport enthusiast who grew up racing Porsches in Porsche Club of America club racing events and has raced professionally in the World Challenge road racing series.
Schardt highlighted several points that should be considered by any enthusiast who lines up to navigate the corners. But citing the big horsepower and massive traction found on today’s muscle cars, his primary concern is strength and safety. “Today’s muscle cars make lots of power,” he says. “The supercharged Camaro that I just recently sold made 550 horsepower when I owned it, and the new owner has already upgraded it to over 600 horsepower at the wheels. And they are relatively large heavy cars.” (Editor’s note: the fifth-generation Camaro weighs over 3700 pounds.) “So when you combine all of this power and vehicle mass with sticky performance tires, then you’ve got to consider the cornering loads and whether or not the wheels were engineered to withstand these loads. Wheels that cannot withstand the load may eventually break and result in a crash.”
Schardt is quick to point out that Forgeline engineers all of their wheels using computer-simulated finite element analysis and then tests them beyond SAE (Society of Automotive Engineers) standards using real-world load variables. “SAE standards assume coefficients of friction that are too low to account for modern performance tires. So, Forgeline automatically assumes much higher friction coefficients and much higher cornering loads to ensure that our wheels are safe, even on the race track.”
Next on Schardt’s list are the typical performance variables, namely stiffness and unsprung mass. “If we are talking about a high-speed road course, then we really need to consider the wheel’s stiffness. In high-speed corners and braking zones, it is possible for the wheel to flex quite a bit, which creates unwanted compliance and less predictable reactions to driver inputs. With a stiffer wheel, we see less deflection and therefore enjoy more predictable reactions to driver inputs, especially under hard cornering and braking.”
And of course, then there is the most obvious metric: mass. “On an autocross course, probably your biggest performance variable is weight. When it comes to unsprung mass, less is more.” Of course, today’s muscle cars are designed to handle large wheels and tires that tend to be heavier. Schardt tells us, “You’ve got to remember that the wheel corners are not only heavy but also spinning, so they generate a lot of rotating inertia. So as they get heavier, they pick up more and more inertia. And wheels with lots of inertia are harder to turn, harder to stop, and harder to accelerate. So holding traction coefficients constant, lighter wheels with less inertia will turn more easily, stop faster, and accelerate more quickly – which is obviously better for performance.”
Once again, Schardt cites some of Forgeline’s engineering advancements to increase rigidity and decrease mass. He recommends that autocross enthusiasts consider wheels from Forgeline’s Performance or Competition Series, as these wheels are built with a stepped-lip design, which allows the wheel center to be slightly smaller and lighter. Many of their newer designs feature I-beamed spokes that serve to reduce mass while also adding stiffness. And all of their wheels are available with optional lightweight titanium fasteners (which can save an additional pound per wheel). Their GA3R model (within the Competition Series) is even warranted for racing use –a testament to their engineering confidence.
Lastly, Schardt suggests custom wheels that are built-to-order may offer some performance benefits as a result of fitment flexibility that is simply impossible to duplicate with off-the-shelf wheels. “Since we build all of our wheels to meet the customer’s specifications, we enjoy some extra flexibility on fitment issues. So if a customer wants to add a little extra width to run a wider tire or maybe reduce the offset to pick up some extra track width, then we can do that. Sometimes those little specs can add up to real performance benefits.” Plus, custom wheels from manufactures like Forgeline are usually designed with extra clearance to accommodate those big brake kits.
So now you know what to look for in the next set of performance wheels for your performance car: strength, stiffness, light weight, and optimal sizing. For more information on wheel options you can contact Forgeline at 800-886-0093 or visit their website here.
Author: John P. Comeskey