Most days, when the weather is favorable, you can find members of our test team at one or more of our test facilities running all kinds of vehicles through our extensive testing regimen. One of the tests we perform on almost all vehicles is the skidpad cornering performance, which ensures maximum lateral acceleration—the maximum cornering stability that the vehicle can achieve, averaging one full turn when turning left and right. Our testers perform hundreds of skidpad tests every year, they’re experts at it, and they almost always match or exceed any claim made to us by manufacturers about how hard their vehicles will turn. That’s why we were confused when we couldn’t get close to the Corvette engineering group’s max-lat claim for the Z06 with the Z07 track package, which includes the new Michelin Pilot Sport Cup 2 R ZP gummy tires.
Corvette engineers told us that the new Z06 equipped with the Z07 will last up to 1.22 g on asphalt on the 300ft diameter skidpad we’re used to, and we have no reason to doubt their numbers as much as we do. , thorough examiner. But we only saw 1.16 g—a significant difference and well below the company’s estimates. Those are worse cornering numbers than we measured on the previous-generation C7 Z06/Z07 front engine, which lasted 1.19 g. What’s more, we’ve also just run a 2023 Z06 convertible without the Z07 package in the skidpad, and its Michelin Pilot Sport 4S ZP tires have held up to 1.12 g, a huge improvement over the base 1.03-g C8 Stingray performance, which you can expect. feel in your neck muscles. What’s going on here?
Only after the Z07 Vette left ours did Chevy tell us the secret sauce that unlocks its full cornering capabilities. For all our performance tests, which include skidpad roads, we adjust tire pressure according to the manufacturer’s recommendations printed on the plaque located on the door frame or B pillar, or in the owner’s manual. If there are many choices, we will use the high speed and low load specifications. Oddly enough, the Z07 plaque requires that the Cup 2s be set at a cool 35 psi, about 5 psi higher than the Z06’s base tire pressure. Since the tires on both versions of the Z06 are the same size, we wondered if something was wrong.
That led us to dig deep into the Z06 owner’s manual where we found a hidden suggestion: owners should lower the Cup 2 R’s tire pressure to 24 psi for maximum cornering on the track. Hah? It took discussion with Corvette engineers and engineers from tire maker Michelin to fully explain the situation.
The reason why Cup 2 tires are supposed to run on the road at 35 psi instead of 30 psi of base tires has nothing to do with handling, ride or fuel economy but rather wet weather traction. Cup 2s have such a small tread depth—the outside of the tread is basically slippery, like a fully loaded race tire—that they have a hard time getting water out. Inflating the tires up so the extra 5 psi crowns the tread is enough to make a significant increase in their grip on wet roads according to Vette engineers.
But it turns out, counterintuitively, the new Cup 2 Rs provides maximum dry road grip at a lower 24 psi pressure. This Cup 2 Rs is the latest iteration of Michelin’s hottest street legal track rubber. The Michelin guy at the location of the Z06 track event showed us the cut-up wreck of the Cup 2R, which reveals a recent discovery by the company. Previously, the radial belt that supported the tread rubber was laid flat and straight across from one shoulder of the tire to the other. But Michelin found that applying a slight wave to the belt acts like a corrugation in cardboard, stiffening the tread area in contact with the road and making it flatter during cornering. That change and some revisions to the tread compound not only allow the tire to potentially provide a bit more grip, but also dramatically different performance during track sessions. The previous 2nd Cup grip was notable for dropping off its lofty peak after just a few rounds; these new ones are said to be able to maintain their grip, and hence a constant lap time, through session after session.
We’ll no doubt appreciate that capability when we run the Z06 with the latest Cup 2 Rs at our annual Lightning Lap event. But we wish we had been informed of the inflation pressure information hidden in the Z06 owner’s manual, so that we could provide representative cornering test results for the Z07 track-pack model. After all, cornering grip numbers don’t just matter on the track; they are a point of proof for makers and enthusiasts of ultra high-performance cars.
We just needed to get another Z07 back in the office as soon as possible to run our skidpad tests again. We can think of much worse ways to spend an afternoon.
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