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Rob's Garage

How many winter tires do you need? Add to ...

Hi Rob,

I have a 2009 Toyota Yaris 4 door hatchback. I just bought it in July with regular summer tires on it. Is it better to put all seasons on the car, or snow tires? Should I buy two or four tires? And if you recommend snow tires, should I buy steel wheels to put them on, instead of changing the wheels and tires in the spring and fall?

I would appreciate your advice, Sue

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The best scenario would be to purchase a full set of winter tires. The old term of "snow tires" does not accurately describe the new technology found in modern winter tires. Years ago, tire manufacturers made "snow tires" out of the same compounds used in their summer line-up, just changing the tread pattern.

In the late 1980s, that all changed with Bridgestone's introduction of the Blizzak line of winter tires. To an untrained eye, they looked like snow tires, but closer inspection reveals a major difference. Most noticeable are the myriad slits across all of the tread blocks.

You will also notice in the picture above that the tread blocks are irregular, jagged edged and somewhat random in placement. Tire manufacturers realized that jagged edges will grip better than smooth symmetrical tread blocks.

Jagged tread blocks work well in snow and slush, but what about ice?

Tire performance on ice is an entirely different issue. When ice is exposed to pressure, heat is produced (and you thought those physics classes wouldn't come in handy). It doesn't take much heat to cause ice to melt, and when it does, a very thin layer of water is created.

To illustrate what might happen to the traction of a tire on ice, separated by a thin boundary layer of water, place an ice cube on your kitchen counter. After a second or two, give the cube a flick with your finger and then try to catch it before it blasts off the other end of the counter.

You will quickly get the idea of boundary layers of water. To solve the problem, get rid of the water.

Tire manufacturers now build tiny channels, or sipes, into tires, so water between the tire and the ice has a place to go. Then the tire can do its job by connecting directly with the now-dry ice, which is quite sticky.

Winter tires also use a rubber compound that remains soft enough at low temperatures to conform to the ice surface, and rough enough to work with the stickiness of the ice. All-season tires will start to harden at 7 degrees Celsius, while winter tires remain flexible at temperatures as low as minus 30 Celsius thanks to various technologies employed by manufacturers.

The bad news is that the softness of these tires makes them susceptible to accelerated wear. So in the spring, get your high-tech tires off and stored away from sunlight.

Concerning your question about steel wheels: Yes, do your new tires a favour and have them mounted and balanced on a dedicated set of wheels. You will accomplish to two positives:

1. Avoid stressing your tires by not having to mount and dismount them two times per year

2. Prevent corrosion of your expensive aluminum alloy wheels (if so installed).

Now that you know what winter tires can do for your safety on the road, the solution is clear: Buy four winter tires and have them mounted on steel wheels.

 

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