By Jim Kerr
With the sun shining and temperatures warming up during the day, it feels like we should be simply enjoying the fall weather, but it is also time to get around to those fall chores like raking the leaves and cleaning the flower beds. Getting your vehicle ready for winter is one of those necessary tasks, but we often overlook it until something goes wrong.
Spending a few minutes checking fluid levels, belts, lights and cleaning battery connections goes a long way to preventing trouble down the road. Changing to winter tires is also an important task that more and more Canadians are performing. Starting in 2008, Quebec even made it mandatory for drivers to have winter tires on their vehicles from November 15 through April 15 of each year. J. Konick, Head of a Quebec task force on road safety, says about 10 per cent of Quebec drivers haven’t been using winter tires, but they are involved in 38 per cent of winter accidents on the road.
Most drivers think winter tires are built for traction on snow and ice, and they are correct, but Pirelli research shows that winter tires are really tires for cold weather, even when there is no snow and ice. As temperatures drop, tire compounds become stiffer and don’t conform to road surfaces as well. Acceleration, braking and cornering ability all decrease. Summer performance tires are affected the most, but all season tires also become less pliable as temperatures drop. Winter tires use different compounds that remain much more flexible in cold weather and that is part of what gives them superior traction when temperatures drop.
Instead of waiting for that first snowfall, Pirelli suggests that seven degrees C is the temperature where drivers should be switching to winter tires. Above that temperature, the tread compound of a winter tire can wear quickly, although they still meet all tire safety requirements and can be driven on the highway at normal speed. Below that temperature, the winter tires quickly begin to outperform other types of tires, providing the traction and safety drivers want on cold road surfaces.
Four areas of winter tire design help provide traction. Tread design, such as grooves, block layout and pattern provide about 50% of the traction on fresh snow, but this quickly drops off as the snow packs. By the time it becomes icy snow, the tread design helps very little with traction. The tread compound provides about 40% of the tire traction and this remains remarkably consistent in most road conditions, from fresh snow to icy packed snow. The compound benefits only begin to decrease when driving on black ice (ice on the road you can’t see), where the compound may only provide about 10 per cent of the traction.
Sipes, those little cuts you see on the surface of the tread, can provide up to about 40 per cent of the traction on packed and icy snow. They work in two ways. First, they have many small edges that can grip the slick road surface. Second, water between the tire tread and the ice surface can be picked up in the sipes so that the tire isn’t “floating” on the ice. Wet ice has to be the lowest traction surface we drive on! Winter tire engineers concentrate on providing a tire design and compound that will remove water from between the tread and the road.
Finally, there are studs. Studs are metal pins inserted into the tread block that dig into the ice for additional traction. Studs work well on black ice, but provide little benefit on snow. As temperatures drop and the ice becomes harder, especially below minus 20, the studs will have less effect even on ice. Studs are also noisy, clicking along the road, and wear the road surface. Many areas of the country prohibit studded tires except at certain times or areas.
I asked a tire engineer with one of the tire companies what the best winter tire on the market would be. He answered me honestly, saying that probably the newest tire on the market would likely be the best. He based this on the rapid changes in rubber and tire technology. Newer tires simply have newer technology, but no matter what you choose, any winter-specific tire will outperform even the best all-season tires when temperatures drop.