How long would you stay upright if you wore leather-soled dress shoes on a snow-covered sidewalk? That's exactly what you are doing if you 'dress' your car in all-season tires.
Graeme Fletcher, Canwest News Service

Published: Friday, November 14, 2008

Of all of the components that make up a car, the tire is usually the most ignored and underrated.

These black doughnuts give the vehicle the ability to accelerate, steer and stop with four small contact patches that, when combined, have an area about the size of an 8 by 11 sheet of paper.
When the weather is warm and the road is dry, almost any tire will deliver some grip.
However, when the temperature drops and the road is covered with snow, only a winter tire can deliver the right amount of grip and traction -- the difference is dramatic.
On a snowy road, a vehicle wearing winter tires has a 38-per-cent less chance of being involved in a collision than a vehicle wearing all-season tires. The fact that the winter tire's stopping distance is 38 per cent shorter than an all-season tire under the same conditions probably has a lot to do with it.
Temperature, ice and snow all have an enormous effect on a tire's ability to function. An all-season tire in the middle of August may be the right one because it delivers plenty of grip on dry pavement and it offers wet-weather traction. Its ability to function begins to deteriorate at around 7C. In the middle of December, on a -5C day, it is next to useless because the rubber has become so hard it has about as much grip on a cold road as a hockey puck has on ice. The closed tread pattern also means the tire is easily clogged with snow, which exacerbates the problem.
A winter tire's tread is made of a much softer compound, so it remains pliable well below the freezing point, which helps maintain the desired level of grip. Its open, aggressive tread pattern also means it has the ability to bite into the snow and keep the tread clear. The downside is the wear rate -- you'll turn a set of winter tires into dock fenders in one summer season.
The best way of thinking about the differences between a winter tire and an all-season tire is to take a look at your footwear. Most would not venture out on to a snow-covered sidewalk wearing leather-soled dress shoes, but that's exactly what happens when the car is driven while "wearing" all-season tires.
Perhaps a bigger mistake is mixing and matching all-season and winter tires -- the practice of putting winter tires on the drive wheels and leaving the all-season tires on the other wheels.
In this case, wearing a winter boot on one foot and a dress shoe on the other. Walking on dry pavement, both shoe types provide enough grip that the risk of slipping is slim. This mirrors the winter/all-season tire situation.
Now, throw in a sprinkle of snow. Walking at a brisk pace, the dress shoe slips and slides, making it difficult to keep one's footing; the winter boot is dealing with the conditions just fine.
Start jogging and landing flat on your face is all but inevitable because the dress shoe will slide out without warning. This is exactly what happens when tires are mismatched, especially on a front-wheel-drive vehicle.
The problem is that the driver only gets feedback from the front wheels (they do all of the accelerating and steering as well as the majority of the braking). If the front tires spin on takeoff, the communication is loud and clear -- the road is slippery. The danger is that the driver gets absolutely no feedback whatsoever from the rear tires until it's too late. This is why so many cars spin in winter. Equipping the vehicle with four winter tires solves the problem.
If the front tires are handling the conditions, the rear tires are doing just as well, if not better, because they don't have to deal with the steering and acceleration forces. All of this applies equally to rear- and all-wheel-drive vehicles.
What's the point of driving all four wheels if only two can put the power to the pavement?
Having decided to buy winter tires, there is one further consideration -- whether to buy a second set of rims or not.
While it may appear to be more cost effective to buy winter tires and have them installed on the car's original rims, it is not the smart or economical solution. Not only do you pay for the cost of installation when the tires are switched (all-season to winter in late October and winter to all-season in March), each wheel needs balancing and the valve stems may need replacing. The other risk is that repeatedly switching the tires on an aluminum rim will cause damage. Every time the tires are changed, it becomes more difficult to seal the tire to the rim. Buying a second set of steel rims and installing the winter tires on them solves the wear factor and makes the switch cheaper (it now costs about the same as a simple tire rotation).
Winter tires make so much sense and yet are so overlooked. As few as 29% of all the vehicles on Ontario's roads wear winter tires. Yes, there is an up-front cost, especially if you make the right decision and mount the winter tires on their own rims. However, that cost pales in comparison with the number of hard-earned loonies it takes to repair the car because it could not stop.
 
© The Ottawa Citizen 2008
 
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