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How It Works

How winter tires differ from snow tires Add to ...

There are two factors that determine how well a tire grips the road – tread compound and tread design.

The compound is made up of a mixture of products, chemicals and production methods. The design is not only what you see, but the structure of the tires beneath the tread.

In the old days, a winter tire was called a snow tire and it had a much more aggressive tread pattern designed to cut into snow. Many people still use the term snow tire – but in reality tire companies no longer offer such a product.

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As chemistry and production became more sophisticated, so did tires. The old snow tire was replaced by the winter tire. The difference was a tread designed to grip both snow and ice and remain supple in cold conditions.

These are critical factors. That old snow tire may have bitten into deep snow thanks to those big lugs and deep, wide grooves. But it got hard when cold and was not as good as a summer or all-season tire in wet or dry conditions, especially on ice.

The development of winter tires involved more closed tread patterns that remain supple in cold conditions and project thousands of little edges to grip ice. Because they do not stiffen up and have treads designed to throw off snow, they continue to be effective in snow.

The tire industry considers seven degrees Celsius as a key point. Below that, all-season tires stiffen up and offer much less grip while above that, winter tires become softer and start to wear excessively.

This has led to a new class or type of tire, all-weather, as opposed to all-season. These new tires are a hybrid of sorts, combining a compound that remains flexible in extreme cold with one that does not become too soft in warm weather.

These new tires, generally at the high end of a company’s range, pass all the severe weather tests necessary to wear the “mountain/snowflake” symbol recognized by Transport Canada and the Rubber Association of Canada, yet can be used year-round.

But that is not to say they are the ultimate tire, that they are perfect in all conditions. Once again, we have a compromise.

The compounding and design that allows these new all-weather tires means they re not as supple and suited to extreme cold conditions as a pure, no-compromise, winter tire. Similarly, they cannot hold a candle to quality summer tires in terms of outright grip when turning or braking in hot conditions. Ironically, we have all-season tires that are decent in spring, summer and fall but fall off when it gets cold and all-weather tires that are decent in fall, winter and spring but fall off when it gets hot.

Some like it hot – summer tires; some like it cold – winter tires; and some straddle the fence, not liking it hot or cold. All-season or all-weather, both are compromises. The best and safest solution is two sets of tires, one of which should be winter tires.

With winter approaching, the temperature of the surface of the road in the morning will be single digits, and often below that seven-degree point. A pure summer tire will offer minimal grip at that point and an all-season tire will be falling off while winter and all-weather tires will be coming into their element.

Do not associate the need to change tires with the arrival of snow. The critical issue is temperature. That’s why consumers should stop thinking and talking about snow tires and switching to winter tires.

globedrive@globeandmail.com

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