Z-Rated Tire Test: Traditional Summer VS New All-Season Performance

With the booming popularity of all-season tires in general and all-season "ultrahigh-performance" tires in particular, many enthusiasts are wondering what they would get-and what they'd have to give up-by swapping their Z-speed-rated dedicated "summer" performance-priority tires for the new breed of all-season ultrahigh-performance tires. And some Sunbelt drivers question if they could get away with the reverse swap: from original-equipment all-season to traditional performance tires. To answer those questions, we commandeered Michelin's Laurens, South Carolina, proving grounds, a trio of performance cars-a Corvette coupe with the Z07 autocross handling package, a Camaro Z28 convertible, and a Ford Probe GT-and several stacks of Michelin's new XGT Z4 all-season performance tires and its proven Pilot SX MXX3 "summer" performance rubber.

With a thorough investigation of one tiremaker's summer and all-season rubber, we hoped to come away with impressions that would apply not only to Michelin's premium offerings, but that also would characterize the upper end of other maker's product lines. For our evaluation, each car was fitted with same-as-stock sizes for this test. The objective performance numbers offered here were obtained by Michelin test drivers using the company's test equipment and should only be used to compare these two tires. "These numbers are valid today, in this environment, on these cars, on these surfaces," said one Michelin engineer. "The differences between the two will remain fairly constant, but the ultimate numbers will vary." All objective tests were not conducted on all three test cars, but a decisive outcome can be culled nonetheless.

The short answer: Switching from traditional performance to all-season performance-or the reverse-is far more pivotal than most imagine. Each tire offers easily noticeable benefits and equally notable trade-offs. The benefits will appeal to some and not to others, and the trade-offs will be accepted gladly by some and vigorously rejected by others.

The Tires Michelin says its Pilot SX MXX3 is designed to "provide ultimate levels of handling and wet traction." Translation: In the compromises-required world of tire-tread compounding and carcass construction, the MXX3 grips as if your car were fitted with an invisible Indy-car wing and provides hard-wired-to-your-brain feedback. Unavoidably, this comes at the expense of ride comfort, wear, and cold-weather aplomb, among other factors. Impressive wet-weather performance is enhanced with wide circumferential grooves to allow the tread blocks to reach the pavement, while angled grooves on the shoulder help wet cornering. Available in 20 sizes-from 205/50ZR15 to 325/30ZR18-the MXX3 is standard equipment on the BMW M3 and the Toyota Supra Turbo, among others.

The XGT Z4 is an exception to conventional wisdom, which says tire construction is a zero-sum game: To gain attributes in one area, qualities must be given up in others. By adopting what its engineers call new compounding "theology" for the XGT Z4, Michelin has enlarged the performance envelope somewhat, retaining the dry and wet traction that's usually sacrificed to attain the snow traction necessary to earn the "all-season" name. Unlike the MXX3, the XGT Z4 features a directional tread pattern. It's available in seven sizes, from a popular 205/55ZR16 to 275/40ZR17.

Both tires have two-ply casings and steel belts topped with a circumferentially wound nylon overhead ply. The nylon ply reduces expansion at high speeds and, when compared with the conventional single-sheet ply, improves production uniformity by eliminating the ply overlap.

The TestsAlong with a host of subjective tests, we conducted four objective tests: deep-water (3-5 millimeters) cornering on a smooth, polished concrete skidpad; dry cornering power on a smooth asphalt skidpad; shallow-water (1.5 millimeters) stopping distance on smooth asphalt; and dry stopping distance on smooth asphalt.