It all comes down to two sets of digits. Some might say that’s oversimplifying, but the radical improvements in the new Corvette Stingray chassis can be summarized with the figures 57 and 99. These numbers refer, respectively, to the percent of increase in rigidity, and the concomitant reduction in poundage. Taken together they’re even more remarkable, because you’d expect that paring nearly 100 pounds off a frame would result in less torsional strength, not more. And certainly not in a magnitude of more than half again as much.
Switching from steel to aluminum frame members helps to explain this feat, yet that too risks oversimplifying matters, as using a lighter, stronger material alone didn’t do the trick. Balancing light weight and high rigidity in the same foundation is a bit like juggling fire and ice, two competing concerns. To find out how this Corvette alchemy was achieved, and the level of precision required, we spoke with a couple of GM insiders: Michael Bailey and Ed Moss.
02] Did someone say “diagnostic equipment”? When it comes to monitoring test-vehicle dynam
Bailey is a systems engineer who oversees multiple areas. His job is to make sure all parts of the ’14 Corvette Stingray’s frame—tires, wheels, steering, suspension, and more—work together in unison for optimum performance on both the street and track. He’s also a Corvette enthusiast, stung early by the Corvette’s allure. His dad still owns the ’61 model that he purchased in 1970, along with a ’69 Corvette 427. The father-and-son team are currently restoring a ’63 convertible.
“I care a lot about the image of the Corvette, and I know what it’s about,” Bailey notes. “I knew it growing up, but [having worked] on Corvette since 2007, I think I understand what the customer is really after.”
Ed Moss is a veteran engineering group manager, having worked exclusively on the Corvette program in various capacities since 1988. “If you’re going to have a narrow focus, what better than on a Corvette?” he laughs.
He’s essentially an analysis guy, with particular expertise in the body structure. By way of clarification, this reference might sound a bit unclear, since we’re focusing on the Corvette’s frame in this portion of our series on the Stingray. But considering how today’s unibody designs integrate both body and frame, the nomenclature makes more sense.
Moss delineates the Corvette’s overall structure into three main areas: the aluminum frame, the carbon-nano unibody panels bonded to this frame, and the bolt-on body panels. Breaking it down further, he says the frame itself consists of, “Two crash cans [cradles], two chassis nodes, and hydroformed aluminum rails.” We’ll be touching on each of these, but before doing so, how do GM engineers go about creating a clean-sheet chassis?
As with the body and interior design, it all starts with computer modeling, Moss explains. But what’s different in this portion is setting targets for torsional stiffness. The C6 already hit an impressive figure of 9,000 N•m/deg (Newton meters per degree, with each unit equal to about 0.737 lb-ft of force). But the computer projections on the C7 raised the bar substantially to 14,500 N•m/deg, achieving that astounding 57 percent increase mentioned at the outset.
While the reasons for doing so are fairly obvious, they bear highlighting. Less weight means multiple advantages in quickness, handling, and durability. On the other hand, for a chassis engineer, having a stiff, strong foundation is absolutely essential for maintaining precision suspension geometry in a high-performance application.
A heavily disguised C7 test mule undergoes a chassis evaluation on one of GM’s four-wheel
How close did the computer projections come to real-world results? To find out, GM did five rounds of static stiffness testing over a three-year period at Pratt & Miller, and they came as close as within five percent of what the CAD system indicated, Moss says. He points out that all of the C6 and C7 models basically have the structure of a convertible (except for the fixed roofs of the C6 Z06 and ZR1), and the new Stingray benefits from an extra measure of strength. How that was achieved involved using several different approaches and materials.
One way it was enhanced was by completely redesigning the center tunnel, including its close-out panel (basically a box-shaped structure). Simply moving it below the exhaust system increased torsional strength in that area by 20 to 30 percent.
In addition, previously on the C6 Z06 and ZR1, the frame had a constant gauge of 4mm from front to back, so “it was carrying mass in areas that you don’t need,” Moss observes.
On the C7, however, engineers varied the gauge of the aluminum frame from 2mm to 11mm, depending on the location, so it not only dropped pounds, but also enhanced stiffness in specific areas. Note, too, that rather than one-piece hydroformed steel rails, the C7’s chassis has a much more complex assembly, consisting of an extruded crash structure up front, a casting where the cradle mounts, tubing next to the cockpit, another casting for the rear suspension cradle, and a rear crush area.