You can judge a tire by its cover
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Even a sports car benefits from true winter tires. In fact, they improve driving so much you can get sports tires fully rated for snowy and icy conditions.
You may not be able to judge a book by its cover, but you can sure tell a lot about a tire by its outward appearance.
A good winter tire will offer a number of characteristics, easily identifiable by its tread pattern and other distinguishing marks.
John Mahler's Top 10 winter tire choices
Okay, some are not visible to the naked eye but the benefits are enormous.
You will find myriad tread block designs. On those treads you will see lots of sipes (razor-like cuts); wide grooves between the blocks; and, for good measure, some microscopic air bubbles in the rubber, which has been specially compounded to stay flexible when frozen.
Each of these elements has a specific job to do in the winter, but the tricky part is that many of these elements work against one another. So the ideal tire for all conditions does not exist. For example, one person's ideal tire may not be suitable for a neighbour whose vehicle, driving style, road usage and routes may be totally different.
Keep in mind that in Canada, we get many days of severe weather, so don't listen to any salesperson who tells you an all-season will work in our climate. For winter, for your safety, you need a winter tire. End of story.
Here's what goes in to making a good winter tire.
Building blocks
The ideal tire starts with just layers and layers of tread rubber. This round block of rubber would be stable under the worst loads the car could put on it, but as soon as the factory cuts tread blocks into that ideal tire, to allow water to escape, it creates instability.
The bigger the grooves between tread blocks, the less support the blocks have. So when your car goes around a corner or stops under heavy braking, the blocks flex, which you feel in your vehicle as poor steering response or shakiness under braking.
Constant flexing of tread blocks also causes premature wear. If the space between blocks is smaller, when the blocks flex, they can lean on each other for support. This mean less flexing, which gives better tread life, but it also leaves less room for slush and water to escape.
Sipes
One way out of this dilemma is through the use of sipes. Sipes are the little wiggly lines in the tread blocks; they look like cuts.
When we see them, they are closed so they don't look like they do anything. But as the tire rotates, the vehicle's weight causes these sipes to spread open into little cavities. Tread pressure pushes water droplets into the space. Then as the tire continues its rotation, the sipes close up and the water is squirted out the back face of the tire.
Tread on this
The tread block shape is very important. Grip in snow is improved by having as many sharp edges on the block as possible. A five-sided tread block has more edges than a four-sided one. A tread block that is jagged instead of straight is even better.
Another sign of a good winter tire is tread blocks on the edge or shoulder of the tire that stand out sharply.
The edges cut into the snow; the tread face compresses it until the car is on temporarily solid, hard-packed snow. So now there is something solid under the tire for traction. Snow, when it is compressed like this, returns to water so the snow gets sticky – snow sticking to snow works very well for traction until the area between the tread blocks is full.
But then the tread area must clean itself. In order to do that, the rubber must flex as the tire rotates. The flexing of the rubber shoots the snow out from the tread so the sharp biting tread block edges are exposed again for the next big bit of snow or slush.
Of course, roadways are sometimes bare. For cold bare pavement, big tread blocks or tread with smaller grooves are best. Less tread squirm makes for comfortable cruising in winter time.
Shopping list
Before heading out for the tire dealer, make a shopping list. Write down all the things that worry you about winter driving: ice, deep snow, wet snow, slush, frozen pavement and whatever else you can think of. Then give them priorities. The list will now tell you what kind of winter tire is right for you.
If ice tops your hit list, then a multi-cell rubber tire is the answer. Here's why: Water always forms on ice when weight, such as that of a car, is applied to it. As little water as a 10-micron deep film can cause traction loss (a micron is one millionth of a metre or .000039 of an inch).
Multi-cell tires have microscopic air pockets mixed into the tread rubber, sort of like the holes in Swiss cheese. These pockets allow the thin film of water a place to retreat so you get good rubber-to-ice contact.
If deep snowy conditions are the main concern, a deep tread with wide channels is the best bet. This is the biggest category of winter tires.
No matter what conditions you encounter, there is a winter tire to get you safely where you need to go. And remember the worst, cheapest winter tire is better than an all-season tire when the winter wind howls and the roads are slippery.
Snowflake Symbol
And last, consider only tires that have the Rubber Association of Canada and Transport Canada's winter tire pictogram on the sidewall. This line drawing of a mountain with a snowflake inside it means the tire has been approved for severe winter use.
Though some tire shops might tell you that a tire without the symbol is still 99 per cent as good, it isn't true. There is no graduated scale; it is a pass/fail test.
John Mahler's Top 10 winter tire choices
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