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Summer Tires in SnowNotes From the Road

Summer Tires in Snow
By Mac Demere/

Frighten Yourself at 15 MPH -
Driving on ultra-high performance tires on a snow-covered road is like trying to negotiate Copper Mountain's expert-level "Drain Pipe" ski run on water skis. Both are skis: What's the problem? Even on tires billed as "ultra-high performance all-season," driving in the snow is like negotiating that black-diamond run on cross-country skis: It's possible, but it's not the best choice.

Also known as "max performance summer" tires or, more accurately, "three-season" tires, they come standard on every Porsche (except the Cayenne), all Corvettes, the Viper, all Ferraris and more. The reason: Summer tires offer more grip—on both wet and dry roads—than all-season tires, much less winter (aka "snow") tires. The only exception: When the thermometer drops below freezing or snow covers the pavement.
Tire Differences
A main difference among winter tires, all-season-tires and summer tires is the pliability and durability of their rubber at different temperatures. Tire engineers call it "glass transition temperature:" Get them cold enough and every tire will have the grip of a Formica kitchen counter. For a race tire, it might be 40° Fahrenheit. For a winter tire it could be 60° below zero. Summer tire tread starts becoming Formica-like somewhere just below freezing. Most all-season tires are still pliable below zero, but some "ultra-high-performance all-season" tires start losing grip well before that.
Grip and Sipes
Tire grip in the cold is much like oil viscosity, largely because tires contain many petroleum-based products. A 50-weight racing oil will protect an engine at temperatures approaching 260°, but at 70° it's almost as thick as Jell-o. Today, most racing oils are "multi-grade": A 20W-50 racing oil remains liquid enough to adequately lubricate the engine while it warms up but still protects at prodigious temperatures. Tires haven't advanced that far.
There are many other things that give tires grip in the snow. "Sipes"—small slices in the tread—are among the top features. But you can't put enough sipes in a summer tire to give it useful mobility in the snow.

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