By Jim Kerr
Winter is making its first appearances across the country and more drivers than ever before are switching to winter tires – but many drivers with 4X4 trucks and SUV’s don’t think they need winter tires. After all, don’t they have the traction they need with all wheels driving?
While most drivers install winter tires because they want to avoid becoming stuck, the biggest advantage of winter tires is accident avoidance. The extra traction works equally well when stopping and accelerating. The superior lateral grip helps keep the vehicle under control, so spins and slides are less likely.
Trucks are more likely to lose control because of the uneven weight balance on the axles, and they are actually worse in 4X4 mode than in 4X2. In 4WD, both the front and rear axles are locked together in the transfer case and operate at the same speed. This is fine if all tires are exactly the same size and you are driving in a straight line, but not all tires are exactly the same size – there will always be a little slip from the tires when in 4X4 mode. Slip means a loss of traction. Turn a corner and the tires follow a different arc, causing them to try and rotate at different speeds. Since they can’t in 4X4 mode, some of the tires break traction and the truck can spin.
Automatic transfer cases are better, because they let the vehicle operate in 2WD unless the extra traction is needed. Back off the throttle and it quickly reverts to 2WD mode, which will cause fewer spins in corners. All-wheel drive vehicles use a transfer case that allows the front and rear axles to operate at different speeds, but even then the advantages of the extra traction during stopping and cornering make winter tires desirable.
Install four winter tires for the best stability. Installing only two tires can cause one end of the car to loose traction on corners. The cost of even a small accident is much higher than the price of a set of winter tires. Think of them as a little extra insurance.
A few years ago, you wouldn’t find much on the market for winter tires other than aggressive open lug types. Now, almost all tire manufacturers offer specialty winter tires for passenger cars, light duty trucks and SUV’s. Most of the manufacturers refer to their best winter tires as “ice radials”.
Some tires are called winter tires because they have the Mud and Snow (M + S) on the sidewall. They sound like they should be good for snow, but the M + S designation is not regulated and you can find it on all kinds of tires. Some work in snow; others don’t. To reduce the confusion, the Rubber Association of Canada has developed severe snow tire performance standards and a Mountain/snowflake icon for the tire sidewall to identify true winter tires. Current winter tires often look more like summer performance tires. It’s the technology that gives them the grip.
More compliant rubber compounds provide much better traction, especially at lower temperatures, but that is only the beginning of winter tire technology. Tread design gives the tire mechanical grip on the snow and ice. Look at a winter tire and you will see small, close together tread blocks with lots of biting edges and wedge shaped openings between the blocks to grip loose snow. This design also has the added bonus of being quiet at highway speeds.
Winter tires also have thousands of tiny cuts in the tread surface. These are called “siping” and provide extra bite on slippery icy surfaces. The siping is often made in several directions, so the tire will have good cornering traction as well as straight-line traction.
Studded tires do offer excellent traction on ice if they are in good shape, but they are noisy and wear the pavement. Most provinces do not allow studs at all, or only allow them during the winter season. Winter ice tires work almost as well as the best studded tires, so I would avoid the hassle of studs.
In reality, there is usually less than $100 difference in price for a set of four premium winter tires versus less capable ones. The extra safety is definitely worth the slightly higher price. There are many brands of winter tires on the market. Make sure the tires you choose have the mountain/snowflake icon on the sidewall.