Winter Driving Guide
Remember that first snowfall, the one when you had to climb the Avenue Road hill to St. Clair, or the hills of Mt. Pleasant or Yonge Street?
Most cars were spinning their wheels forward while sliding down the hill backwards. Drivers with winter tires were busy dodging the slow-motion cannonballs coming back at them.
Were you a dodger or a slider? Days like those will make winter tire believers out of almost anyone.
But what about on level ground? All-season tires may not get you stuck, but they also may not get you stopped in time. Tests by the Ontario Ministry of Transportation found that a subcompact car stops 11.6 metres shorter with winter tires than with all-seasons, at minus-20C with 3 to 5 cm of compacted snow on the road.
The speed in question was a lowly 50 km/h. A minivan doing the same test needed an extra 12.8 metres with all-seasons. As the speed doubles, the stopping distance quadruples, so at 100 km/h, the distances become hair-raisingly scary. Try to imagine taking 48 metres longer to stop than the car next to you.
OK, but what about bare cold pavement? Tests I conducted at the DDT track at Canadian Tire Motorsports Park last winter show all-season tires just don’t like grabbing cold pavement when it’s time to stop. At minus-14C, from 80 km/h, the all-season tires averaged 5 metres longer to come to a halt.
Grip is all about friction. A tire’s grip requires that its rubber be soft and compliant to the road surface, so that it molds itself into the road. The tire rubber interlaces with the irregularities of the road surface, locking together for that brief moment in time as the car moves forward. If the rubber is stiff, it does not conform and snuggle into the road irregularities, so it slips.
All tire rubber has an ideal temperature range. Summer tires like it hot, all-season tires like it to be moderate and winter tires like it cold. If a tire’s temperature falls below its ideal range, it begins to stiffen up and lose its elasticity, and the grip goes away.
In comparing all-season tires with winter tires, grip levels on bare pavement are about equal from 0 to 7C. But as temperatures drop below freezing, the all-season tire loses grip and the winter tire gains grip.
All tires, even the best, are a compromise. For every positive engineers create, they create a negative in some other part of the performance envelope. Tire design is like working with a partially inflated balloon, push in on one spot and it bulges elsewhere.
All-season tires are the ultimate compromise: they do most things well but are exceptionally good at nothing. Rubber compound that does not get too soft on a hot July day cannot stay flexible when the temperature plummets.
Once we add hazards such as snow or slush, the all-season tire loses more ground. Winter tires have wider channels for slush removal and sharper biting edges on the tread blocks to cut through snow. And for ice, winter tires have many more of the ultimate weapon — sipes, those little squiggly lines cut into the tread blocks.
A winter tire has all these advantages and it can use them all because it has the flexible soft rubber to maximize its many tools. Meanwhile, the all-season tire is getting stiff and, by minus-20C, is not doing much gripping at all. It has become more like hard plastic than rubber.
Fountain Tire quotes a study conducted by the Quebec Ministry of Transportation showing that proper winter tires can improve braking up to 25 per cent over all-seasons, and can improve collision avoidance by 38 per cent. In 2007, Transport Canada conducted tests in snow that showed all-seasons took up to twice the distance to stop than winter tires.
Properly tested and certified winter tires are identified by the Transport Canada “severe winter use” pictograph on the sidewall, a sharp mountain peak surrounding a snowflake.
There is a new class of tires called “all weather.” These carry the mountain snowflake pictograph but are meant to be driven all year. They do well in moderate snow conditions, especially on vehicles with all-wheel drive, but when the weather gets severe, they do not perform up to the level of a winter tire.
Transport Canada recommends snow tires be installed in sets of four, since vehicle handling is improved when identical tires are installed on all four wheels. Mixing tires with different tread patterns, internal construction or size degrades the stability of the vehicle.
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