In winter, it's all about the tires

Advances like electronic traction control and all-wheel drive make it possible for many cars to get through winter on all-season tires, which provide good grip in a wide range of conditions.

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Advances like electronic traction control and all-wheel drive make it possible for many cars to get through winter on all-season tires, which provide good grip in a wide range of conditions.

But in regions with heavy snowfall and prolonged low temperatures, a set of specialized winter tires may be the difference between getting to your destination or spinning off a slick road.

About 20 years ago, winter tires were much the same as summer tires except for a tread pattern that was deep and blocky – a design intended to help the car claw its way through snow. But winter tires have improved a lot in the last decade or so.

For example, tire engineers figured out how to create minute porosities, openings in the tread material with edges that help to bite the road. The little indentations also create an escape route for the thin layer of water that can form on top of road ice, says Bridgestone, which makes the Blizzak line of studless winter tires.

Another big advance came when engineers began adding silica, a mineral that makes up most of sand, to the carbon-black filler material that gives tires their color. In addition to improving fuel economy by reducing the tires’ rolling resistance, silica also improves wet traction. It has a third useful trait: improving the low-temperature flexibility to help maintain winter grip.

“At around 44 degrees Fahrenheit (7 degrees C), the way rubber compounds behave significantly changes,” said Parmeet Grover, Michelin brand director at the company’s United States headquarters in Greenville, S. C. “They become much less pliable.

“Special winter tire compounds are formulated to push that transition temperature down lower,” he added. “Silica is a part of this, and the rest is the black magic of compounding that we keep to ourselves.”

There is another benefit to adding silica to winter tires: they last longer than the older, fast-wearing snow tires.

Early silica-compound tires didn’t have such great life, either.

“The silica wouldn’t bind to the rubber polymers,” said Steve Carpino, vice-president for research and development at Pirelli Tire North America.

“Now we have additives that give silica and polymers in the compound the bond you need for good wear. Tread patterns have gotten a lot better, too.”

Because there are so many choices of winter tires, selecting the appropriate ones can be daunting.

The first consideration depends on typical winter weather conditions. Drivers in areas where winters are cold but generally dry can use a winter performance tire, which provides traction that is nearly as good as that from all-season tires. But in regions where snow covers the ground for long stretches, a true snow and ice tire is preferred.

A good starting point is the Web, where the sites of tire makers and large retailers offer useful guidance on selecting tires along with their sales pitches.

Tire makers often recommend that drivers buy four winter tires, rather than just put a pair on the engine-driven wheels.

Sure, these people are selling tires, but there are sound engineering reasons for the advice. Antilock brakes, traction control and other electronic safety systems make their rapid calculations and interventions on the assumption that the car has four tires with the same performance abilities. Conflicting information from a mixed set of tires can confuse the systems’ judgment.

All-wheel-drive vehicles, too, can benefit from a full set of winter tires. Engine power at all four wheels can help a vehicle accelerate from a stop, but will not help it stop. That depends on friction between the tires and the road.

Changing to winter tires necessarily requires compromise. The tread pattern may make them noisier, the ride may be somewhat harsh and the cornering on dry pavement will suffer. Typically, winter tires carry a speed rating a step lower than the one on the summer tires they replace.

Owners of vehicles factory-equipped with run-flat tires, which are not equipped with a spare, may need to make an accommodation when a change to winter tires is made, such as adding a small compressor and a sealant kit to the trunk – or signing up for a roadside assistance program.

Owning two sets of tires for one vehicle may seem extravagant, but consider that all the months it is running on winter tires, the summer tires are resting in the garage, not suffering any wear at all.

Winter tires should last three seasons if they are removed as soon as the weather turns warm.

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