Jan 22, 2021
8 min. read
Most drivers know when the mercury regularly dips below 7 degrees Celsius, it is time for your car to wear its winter tires. The rubber compounds from which a winter tire are made contain elements that allow them to remain pliable in cold temperatures. Stiff rubber simply doesn’t offer as much grip; put on a pair of flip flops during the next ice storm to discover what we’re talking about.
You'll notice throughout this article we've called them winter tires and not snow tires. That's because their unique design and composition work best at temperatures below 7 degrees Celsius. In other words, roads don't necessarily need to be snow-packed and icy for drivers to realize the extra grip provided by winter rubber.
Still, winter tires aren’t a lot of help if they’re too smooth. Making sure your tires have the proper and safe level of tread depth is easy.
How to check your treads.
To check the tire's tread depth with a proper gauge or have them looked over by a technician. A depth of 4mm or less is skating on the edge of usability; most winter tires roll out of the factory with a tread depth of 10mm or more. If you have access to a handheld tread depth gauge, be sure to check multiple locations across the tire's width. If a tire has been wearing unevenly, it may earn a passing grade on its inside edge but flunk the test on its outer edge. Those of us without a tread depth gauge in their toolbox should visit an AARS-approved shop or a trusted mechanic for advice.
Tires also have built-in indicators called wear bars. They are small ribs of non-structural rubber that span the gap between those meaty tread blocks. They’re hard to see when there is a lot of tread but become prominently visible when the tire becomes worn to the point of needing replacement. Some brands, Nokian in particular, mold the numbers 80/60/40 into the rubber. They represent the rough amount of remaining life and slowly become visible as the tread wears away. Many winter tires start life with a tread depth and approximately 10mm and most experts advocate for their replacement when that number is down to approximately 4mm. This is much different from all season tires whose legal replacement limit is 2/32”.
Composition of a winter tire.
A quick lesson, in case you fell asleep in class: mechanical attributes (the tread pattern) and molecular construction (the rubber compound) are the two features that separate a winter tire from an all-season hoop.
The first is easy to visually see. It’ll not escape your notice that tread blocks on a winter tire are packed with little zig-zag cut features. These are called sipes. They open up slightly when pressed into the road surface, creating extra biting surfaces to provide more grip (the Continental VikingContact 7). A close examination of those tread blocks will also reveal edges shaped like a serrated blade, another design decision intended to create extra grip, not unlike when a cat’s claws dig into the sofa (the Yokohama iceGUARD iG53 tire).
Those who claim all-season tires perform similar to winter tires may try to argue there is little difference in how the two are constructed. In defense, try this experiment. Take a block of normal styrofoam and push it along the surface of your kitchen table. It slid pretty smoothly, right? Now, cut four or five shallow grooves in the styrofoam’s surface and try to push it along the table again.
Different, eh? The extra surfaces you made when cutting grooves in the styrofoam create more area for grip. In the tire industry, these grooves are called sipes. The tread blocks of a winter tire are designed to cut through snow and slush, evacuating the liquid that can get in between the rubber tread and road surface. Using sipes, they create extra contact patch and gripping areas which provide control when accelerating, braking, and turning.
Visually seeing the rubber compound in a winter tire isn’t possible, nor is finding out specifically what the compounds are comprised of. Tire companies play their cards close to their chest, guarding their recipes closer than Colonel Sanders guarded the 11 herbs and spices. Still, if one were to press on a winter tire in the way one would test the freshness of a melon at the supermarket, they’d find it to be much more pliable than a high-performance summer tire.
Molecularly, a winter tire is made up of different rubber compounds than an all-season tire, allowing it to remain a bit malleable when the ambient temperature drops. Without this flexibility, a tire will simply skate over the ice and snow rather than grip it.
What to look for.
For advice in selecting a new set of shoes, we went straight to the top and spoke with Geoff Wiebe, corporate manager at a tire company that's been equipping Canadians and their cars with safe rubber for decades.
"One of the essential things when choosing a winter tire it to look for the severe service symbol," explained Wiebe. "This is what's commonly called the 'three-peak mountain snowflake' should appear on the tire's sidewall." Only tires that pass a strict series of tests about winter grip and durability earn this badge.
Studded winter tires aren't permitted on the roads of southern Ontario but the Ministry of Transportation recently made regulation changes in other areas of the province thanks partly to advancement in stud technology. "If studs are installed when the tire is manufactured, it permits a more advanced design than studs which are put in at a garage." In other words, factory studs are generally kinder to our nation's pavement.
Studs or not, silica-based compounds are the key to a winter tire maintaining its flexibility in cold temperatures while remaining firm in moderate conditions. This allows them to bite into packed snow and find purchase for straight-line and lateral grip. Testing suggests a car on winter tires will stop up to 7 metres shorter than if shod with all-season tires on the same frigid surface.
One final note: always - always - install winter tires in sets of four. The adhesion difference between the front and rear of a car when a driver puts them only on the car's drive wheels can actually cause, not solve, traction problems. CAA is here to help its members, so be sure to call our team of experts if you're seeking further advice on getting your car ready for a safe winter season.
CAA Auto Advice.
Do you have your own car-related questions? We'd like to help.
CAA’s Auto Advice team provides Members with free automotive advice. If you have questions about car care, buying a new or used vehicle, auto repairs, vehicle inspection, driving costs and more, contact our Auto Advisors by phone at: 1-866-464-6448 or email autoadvice@caasco.ca. Our licensed technicians and experts will be able to assist you on many of your of car related questions.