GATEWAY, Mont. -- Quebec's decision to institute a mandatory winter tire law was the right move. On a frozen road, the differences between an all-season tire and a proper winter tire are dramatic. The fact that a car shod with all-season radials is 38 per cent more likely to be involved in a crash under these conditions than the same car wearing winter tires says it all. Technically, the difference between the two tire types boils down to the tread pattern, its compound and the siping (the zigzag, knifelike cuts in the tread blocks). The compound dictates the point at which the rubber turns from something able to grip the road to a near-useless black ring. At 7 C, the all-season's harder compound -- needed to provide the required driving life -- begins to lose traction. At the same temperature, a winter tire is just beginning to get comfortable. At -7 C, the all-season has become so hard it slides like a puck on ice. Conversely, the more pliable winter tire is in its element. The first test at Continental Tire's Extreme Winter Excursion pitted two Ram 2500 4x4 pickups against each other -- one wearing all-terrain tires and the other General Tire's Altimax Arctic winter tires. On a timed run around a twisty snow-packed track, I managed to stuff the Ram and its all-terrain tires into a snowbank. Chalk it up to poor driving and less than adequate traction. Switching to the Ram wearing the Altimax Arctics completely changed the dynamics. There was a faster launch, better turn-in response, shorter stopping distances and no snowbank.- Canwest news service
The most graphic demonstration involved pushing three Mustangs through a double-lane change. The first Mustang was equipped with four all-season tires. The second had all-season tires on the front wheels and ExtremeWinterContact winter tires on the rear wheels. The third car was wearing four ExtremeWinterContacts.
This tire employs dense siping in the tread blocks, which adds the needed biting edges to the compound's ability to conform to the surface. The asymmetric tread pattern then allows the tire to do a number of divergent chores. The broad outside shoulder improves steering response; the inner tread pattern shortens stopping distances while evacuating water/slush or biting into the snow. Trying to drive the Mustang wearing four all-season tires proved to be a futile venture as it took a helping hand to just push the car off the line. Getting up it up to 55 kilometres an hour was just as difficult and, through the lane change manoeuvre, there was an unsettling mix of understeer and oversteer. The seemingly simple task of turning the car around to go back and do the braking portion of the test was just as iffy.
The Mustang wearing the all-season/winter tire mix launched off the line with authority, but it was very difficult to keep pointed in the right direction. It also understeered horribly through the lane change manoeuvre.
Blame the lack of steering grip provided by the all-season tires.
The Mustang wearing four ExtremeWinterContact tires sailed through the course with remarkable predictability -- no surprise here. It was easy to get to speed, directional stability was first-rate and there was little understeer when the car was asked to change direction.
Larger differences in the ability of the two tire types surfaced in the braking portion of this test. The all-season Mustang took three times longer (and that's a conservative estimate) to stop when compared with the Mustang wearing four winter tires. That's the difference between a minor white-knuckle moment and an almighty bang. This, however, was not the largest lesson learned.
The danger of mixing all-season tires with winter tires can be fatal. When driving a car wearing four all-season tires, the driver is only too aware of the dangers because of the complete lack of traction. This brings a built-in safety margin. On the flip side, installing winter tires on the drive wheels and leaving the all-seasons on the other axle instils a false sense of security. A rear-drive car will launch with authority, but when the need to change direction arises, the driver is left hanging out to dry -- spinning the steering wheel left to right does absolutely nothing.