It's that time of year again. Temperatures are dropping and snow is either here or on its way depending on where you live. And that means you should think about putting a set of winter tires on your car.
For many Canadians, buying winter tires is what’s called a “grudge purchase” — we don’t really want to lay out the money unless we really have to. Aside from places where swapping in proper winter tires is the law, that means that we can be lulled into a false sense of security by the “all-season” rating of the tires that we drive on the rest of the year.
It gets even worse when you’re talking about all-wheel-drive or four-wheel-drive vehicles, where manufacturers tout clever limited-split differentials, torque-vectoring capabilities, anti-lock brakes, and complex stability controlling systems. Cars are getting more clever— why can’t we have one type of tire to handle all conditions and let the electronics sort it out?
What's wrong with all-seasons?
You might remember an old Pirelli advertisement from the ‘90s, featuring Olympic gold medal sprinter Carl Lewis crouched in the starting blocks, wearing a pair of high heels. The tagline said it best: “Power is nothing without control.” You can have the best on-board traction systems in the business, but it’s not going to matter unless your car has the right shoes on.
We’re not just talking about snowy conditions either; when the air temperature starts dropping below seven degrees centigrade, it’s time to start thinking about making the switch to your car’s winter boots. Below seven degrees, all-season tires start to stiffen up and lose traction.
Compounding the problem
Wondering how exactly four round black rubber things can differ so much in the way they handle cold weather, rain, slush, black ice and snow? Well, all tires aren’t created equal. Yes, they are (generally) all made of rubber, but down at the molecular level things start looking very different. The polymers that make up a tire can either be synthetic, natural or some blend of the two. They’re manufactured to be springy and elastic, able to be filled with air and work like a tough-skinned balloon for your wheel, maximizing the amount of rubber in contact with the road.
The trouble is, different polymers have different operating temperatures. At a certain point, they start losing their flexible, rubbery nature and harden up. The technical term for this is the “glass transition temperature,” and it can be visualized by imagining what happens to a child’s plastic bucket that’s left out in a cold snap – it gets brittle, and can break if you drop it.
The same thing happens to tires, to a lesser degree. While all-season tires aren't going to shatter when it gets cold, they will start losing their springiness at around seven degrees C. Winter tires meanwhile are designed to be softer at lower temperatures in order to maintain that grip on freezing ground.
If winter tires are softer and provide better grip, you may wonder why we don't simply use soft-compound tires all year round? That answer is simple: when summer temperatures hit, the rubber compound gets so soft it wears out very quickly.
Tread carefully
The second part of what makes winter tires more effective than all-seasons in the cold months, and something manufacturers spend a fortune on developing, is their tread patterns. You can actually hear and see the difference between a snow tire and a summer tire, whether it’s the clearly-visible knobbly design, or the rumbling noise they make as you drive down the highway.
Imagine starting off on the extreme end of the tire spectrum with a soft racing slick (with no tread). This maximizes the tire's contact area with the ground, but when it rains, the tire can’t evacuate the water. A rain tire adds grooves to help channel the water through rather than hydroplaning over it. Drive it in snow, and the narrow rain-channels soon get packed with icy debris, turning the tire right back into a slick! Time to add more – and better – channels. The rugged look of a dedicated snow tire comes down to the increased number of grooves and channels – known as “sipes” – in its surface. The more sipes, the theoretically better the tire is at handling deep snow and slush.
However, that doesn’t mean it’s necessarily the best tire choice for your winter driving as not all winter tires are created equal either. Some are specifically designed to handle heavy snow, others for driving on ice while others are more general purpose aimed at providing better grip than all-seasons in a variety of winter conditions.
When shopping for a winter tire you need to consider what types of road conditions you will be driving most often. In the country, where roads aren't plowed nearly as often you might want to think about a winter tire designed to handle heavy snow. If you live in the city, where the streets are plowed often you might be more concerned about ice.
Whatever choice you make – whether it’s for a longer-wearing cold-weather tire for your daily commuter or a dedicated snow tire that turns your SUV into an unstoppable winter-proof snowmobile – you’ll be far better off than the car stuck on the side of the road with all-season-tires. And, did you know that some car insurance providers even offer a discount for having winter tires?