Why you need four winter tires

This is the time of year when the same discussion is heard in many offices, coffee shops and homes: should I put winter tires on my vehicle?

The answer is a definitive and resounding “Yes,” if you want maximum safety.

Whatever you have on your car, high performance summer tires or all-season tires, you will not get maximum grip on cold mornings unless you are on winter tires.

All tires have a temperature range they like to work in to give you their best performance. Summer tires like it hot, all-season tires like all things moderate and, of course, winter tires like it cold.

No big surprises there. What may surprise some drivers, however, is that all these different types of tires all have somewhat equal grip when the temperature is 7 degrees C or above.

Above that magic number, the summer tire develops grip on a steep curve as temperatures climb; the all-season tire less so.

As temperatures drop below 7 C, however, the winter tire develops more grip, the all-season tire loses grip and the summer tire is just about useless.

As we approach November, when temperatures in the morning will be just above freezing, you can bet that the pavement will be very cold. Winter tires have rubber compounds formulated to stay soft and pliable for better traction in cold weather, something that all-season tries don’t have.

To better understand how traction works, we have to think small. Up really, really close, that smooth pavement underneath your car actually looks a lot like the Canadian Rockies. The pavement is all sharp points, with deep valleys in between; it is a very irregular landscape. A tire’s surface is like that as well, made up of irregular hills and valleys. When the car rolls along and these two surfaces — rubber and road — meet, they must interlace for good grip.

The tire rubber must be flexible enough to wiggle and fit into the microscopic grooves in the pavement. The tire can then achieve maximum contact and use all of its surface to push off as it moves forward. If the tire rubber is not flexible, it cannot get into the microscopic grooves in the pavement. In that case, the contact surface area is just a fraction of what would be possible if the tire was flexible.

Try interlacing your fingers to bring the palms of your hands together. You can see the size of the contact area and how strong it is. That is your winter tire on pavement.

Now try placing your hands fingertip to fingertip. There is little contact area and if one hand pushes on the other, it slips. That is your car on stiff all-season tires on cold pavement. Small surface area equals small friction patch equals small grip.

All of this friction information depends on the pavement area being cold, dry and bare. Now add the lubricating qualities of water or slush or snow and you can see that the grip situation just gets worse.

There are many types of winter tires. Some are designed to be specialists in ice or snow, some are high-speed rated. There are even a few winter tires that can be left on the car year-round.

Current generation winter tires have shed some of the characteristics that annoyed drivers previously. For instance, these tires no longer generate loud buzzing noises at speed on the highway because they no longer have the huge blocks of tread that used to make cars squirm and jiggle whenever the brakes were applied.

If cost is a consideration, remember that your winter tires wear less in cold weather than all-season tires. All-season tires wear considerably faster when driven in winter. A Swiss auto club study showed that total tire costs for a sedan after five years were less when the car switched between winter and summer tires.

Article Information

  • Source: Wheels.ca
  • Author: John Mahler
  • Date Posted: November 3, 2010

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