Enthusiasts often think in simple binaries. Manual transmission good, automatic transmission bad; hydraulic power steering good, electric power steering bad. All-season tires fall into the same boat, compared with their more specialized summer or winter brethren. But reality isn’t quite so simple.
Not all all-season tires are bad, just as not all manual transmissions or hydraulic power steering systems are good. There’s certainly merit in having the right tool for the job, but flattening the discussion around an entire category also means some really interesting engineering can get overlooked, like the C8 Corvette’s standard Michelin Pilot Sport All Season 4 tires. These are the first all-seasons fitted to a Corvette from the factory.
“I think there was a lot of discussion and maybe tension within Corvette whether or not they were going to do this,” recalls Steve Calder, ultra-high performance product category manager for Michelin. “Our feedback to them was [based on] listening to their customers for years. A lot of these people would like to drive the car on nice, cold mornings, particularly people living in Canada and the Northern US, but were uncomfortable driving on summer tires in those conditions, and willing to give up a tiny bit of the ultimate performance to get an all-season tire.”
The definition of what constitutes an “all-season” tire is nebulous. Calder says that for Michelin, the goal is to provide “mobility in cold, and light, snowy conditions.” In order to do this, there is a quantifiable threshold the tire must meet.
It’s based on results from a standardized test, ATSM F1805, which measures traction of a single driving rear wheel on snow and ice. In order to be deemed an “all-season,” the tire must perform at 50% of the level of the test’s standardized reference tire. For context, a tire like a Pilot Sport 4S summer tire might only manage 10 or 20% on the test, whereas a tire that has the three-peak mountain designation indicating severe snow rating must perform at least 110% of the reference. The Pilot Sport All-Season 4 in its OE replacement spec scores between 65% and 75%, but Michelin company declined to provide the figure for the Corvette-spec tire.
The Pilot Sport All Season 4 is not severe-snow rated, so don’t take your C8 Corvette out in a blizzard without true winter tires, unless you’re looking for trouble. But if you get a couple inches of snow, you should be all right.
At the project’s outset, Michelin and Corvette came up with another goal for this tire—1g of lateral acceleration on the skidpad. A nice round number that would put these tires on par with dedicated summer performance tires from a generation or two back. And a number that would show the rest of the world that this was a serious effort, not just a half-hearted capitulation to customer demand.
Achieving all these disparate aims, says Calder, comes down equally to two factors—compound and tread pattern.
It’s easy to think that tread pattern is the big differentiator between tire types because, well, that’s the thing we can see. If you put this tire side-by-side with the Corvette’s Pilot Sport 4S and a racing slick, you can immediately establish a hierarchy. All the extra cuts and grooves in the Pilot Sport All Season 4 help boost wet weather performance, and enable some snow-ability. But all that hurts overall tire stiffness, which is why you’ll see far fewer tread blocks on the Pilot Sport 4S, and none whatsoever on a slick, which is optimized for ultimate speed.
So that’s where the compound comes in.
“I used to be a test driver before moving to marketing, and I experienced a snow test with a slick,” Calder recalls. “I thought ‘there’s no way I’m going to get out of the garage,’ and actually, it was mobile. It was all about the compound they had put on there. It really opened my eyes to the effect that compound has on traction, even in snow.”
Compounds are so important, Calder’s not sure what would win in a hypothetical test—a slick with a great snow compound, or a winter tire with a summer compound. Of course, neither would be ideal, but you get the point.
This is also where Michelin can make a big difference for the Corvette’s tires. Like a lot of its tires, the Pilot Sport All Season 4 is a tire Michelin sells in many iterations, and typically, all those iterations will have the same basic tread pattern. When developing a tire for factory fit on a specific car, you keep the tread pattern, but change up the compound and the construction.
Michelin has a proprietary design and production process called C3M, which “allows the designer to put different rubber compounds just about anywhere they want in the tire,” Calder explains. “So whether they want to do a different compound or multiple compounds across the face of the tire if they want to do different compounds as the tire wears down or some combination of both.”
As an example the longitudinal grooves that mostly deal with evacuating water are lined with a winter-tire compound. Traditional winter tires generate snow grip by packing snow into lateral sipes in the treadblocks. The effect is like that of a snowball—snow grips snow. In the Corvette’s all-season, the longitudinal grooves fill up with snow and create that same snow-on-snow contact, generating grip.
Of course, the performance isn’t just down to Michelin either. A program like this represents a collaboration between the automaker and the tire supplier. Both the car and tire are optimized for each other. It’s a virtuous development cycle, each making the other better until the final product is realized. So, a lot of the work was down to Chevrolet optimizing the Corvette to work with what Michelin provided.
I got a chance to drive a Corvette Stingray with these tires a few months ago. Unfortunately, it didn’t snow, so I wasn’t able to test that out, though a video from the excellent Tyre Reviews YouTube channel demonstrates that these tires have the sort of snow performance you’d expect: Good, but nothing compared to a dedicated winter tire. But, I was able to drive the car in a scenario Calder described exactly—a cold, dry day.
The temperature barely exceeded 30 degrees, but the Corvette drove wonderfully. It was right down the middle between a dedicated winter and a dedicated summer tire. You got rubber that didn’t feel all hard and horrible, like a summer tire does in cold temperature, but basically none of the soft, floaty dry handling and slow response you get from a winter tire. Of course, it’s not as sharp as a car on dedicated summer tires in warm weather, but you can’t expect it to be.
If I owned a Corvette, I think I’d still have a dedicated set of summers for warm weather, just for the sake of giving the car that more dialed, on-the-nose feel, but I might run these all-seasons instead of dedicated winters in the cold. For most customers, a Corvette is not a car they’re going to drive in heavy snow conditions in the winter—at most, they’ll take it out when it’s dry, and for that, the all-season works phenomenally.
Calder says he’s seeing more automakers embrace these sorts of performance all-seasons following the Corvette’s lead. Not necessarily on sports cars, but things like sports sedans and high-po SUVs. These are cars where you get a lot of customers who run one tire year round, and moreseo than a Corvette, these are daily drivers, too.
I think what’s possibly more interesting is what comes next. A tire program like this usually starts three or four years before vehicle production begins. When you consider the C8 Corvette went into production in 2019, this tire is, in a way, decade-old technology. So what’s the spread of performance look like in the next ultra-high-performance all-season tire?
If this isn’t the tire to convince naysayers, maybe the next one will.
