Not the old man's winter tires

A very good winter tire can provide 20 to 30 percent more traction than an all-season tire, so drivers who don't make the switch might be stuck with regrets when the weather turns nasty. (Jonathan Kirshner/CNS Photo/file)

Football, Thanksgiving, and snow tires - three venerable traditions of a New England November. At least, they were when I was growing up.

With the invention of all-season radials, you might think that snow tires - now universally called "winter tires" - no longer have a use. But the all-season name is a misnomer, tire specialists say. As Consumer Reports states in this month's edition: "No tire does it all."

If you want more proof, just look north of the border. As of Dec. 15, the Canadian province of Quebec is making winter tires mandatory on passenger cars until spring. The fine if you're caught without them - and police can stop you for having the wrong tires - is between $200 and $300, though the law applies only to cars with Quebec registrations.

"It's for safety," said Paul-Jean Charest, spokesman for the Transportation Ministry of Quebec. "It's proven that 38 percent of vehicles involved in accidents in Quebec in the winter do not have winter tires. For that reason, the government says it would be better to have a law stating that all vehicles in Quebec must have winter tires."

So, what are the differences between an all-season tire and a winter radial? How much more traction will a winter tire give you? What about studded tires? Here's the lowdown.

High-tech turn

Dorchester Tire Service's Alan Saks, who has been installing snow tires for more than 25 years, remembers the days when everybody threw metal-studded snow tires on their two-wheel-drive cars. Nowadays, almost no one uses the road-crunching studded tires (though they are still legal between Nov. 15 and May 1) and no one buys just two snow tires.

"If you have an all-wheel-drive vehicle or front-wheel drive, you must have all four tires matching," Saks said.

"If you don't, the gear ratio is affected, and the braking can be affected. If you have mismatched tires and hit the brakes, the front ones will stop faster than the rears. If there's more traction in one set than another, the car may spin or fishtail."

Back in the old days, snows weren't that much different than standard tires. Your basic snow tire was denoted by the letters "M" and "S" on the sidewall, which stood for mud and snow, respectively. Such tires typically had bigger grooves to give water, snow, or mud a place to go when the tire rolled over a slippery surface. The goal was to eliminate the slippery layer between the tire and the ground, thereby maximizing the amount of rubber actually in contact with the road.

That's still the goal with modern winter tires. But like many other car components, winter tires have undergone a technological revolution. Today's winter tires are made with sophisticated rubber mixtures designed to retain flexibility in subzero-degree temperatures. Some, like Bridgestone's Blizzak series, have microscopic pores to soak up even more moisture and millions of "biting particles" that dig into ice just like studs. Goodyear makes a tire with volcanic ash and glass fibers embedded in the rubber.

A winter tire's tread pattern is also "more aggressive, with more edges within the pattern, and maybe wider-spaced grooves to enhance traction in snow," said Ed Markey, a Goodyear spokesman.

Just how much more traction a high-tech snow tire will give you over an all-season tire is difficult to quantify, mainly because of the variety of tires on the market and because winter driving conditions vary so greatly, said Kurt Berger, manager of Bridgestone's consumer products engineering division. But generally speaking, a very good winter tire can provide 20 to 30 percent more traction than an all-season tire, he said. And possibly more.

"An all-season rubber compound tends to work reasonably well in moderate temperatures. But that compound will become very brittle and rigid in very low temperatures, reducing the traction of the tire," Berger explained. "There's a fairly significantly steep drop-off in all-seasons when you get down in temperature to the 20s and the teens. Summer tires have virtually no winter capabilities once you get below 32 degrees. A winter tire, if you look at both wet and dry traction, remains fairly constant even as you go well below zero."

Conversely, winter tires perform poorly in warmer temperatures, as the rubber compound softens and loses its gripping ability, and they will also wear out faster.

So you don't want to put them on too early, or take them off too late.

"If you're in an area with snow coverage a high percent of the time, the wear rate is very, very low. Your winter tires could last many seasons," Berger said.

Buying decisions

So, how do you choose which winter tire to buy? The November issue of Consumer Reports is certainly one valuable resource, as is TireRack.com, the website of a national tire distributor that conducts its own road tests and posts more than 100,000 individual customer reviews. So is a trusted mechanic or local tire dealer.

I can't recommend one tire over another, but I will offer a caveat.

The M&S marking system is still used today, but it's widely acknowledged as a weak standard for picking a winter tire, since manufacturers can stick the letters on a sidewall without any data whatsoever that the tire has better traction in slippery conditions.

The US-based Rubber Manufacturers Association and the Rubber Association of Canada, recognizing this shortcoming, pushed for a new, voluntary industry standard for winter tires a decade ago. Tires marked with the tiny picture of a three-peaked mountain and a snowflake are supposed to be "designed for use in severe snow conditions." Such tires, when put to a simple braking test on a few inches of packed and fresh snow at 5 miles per hour, are shown to provide at least 10 percent more traction than a standard tire tested under the same conditions.

That's obviously an improvement. But the standard, Bridgestone's engineers said, isn't tough enough, as even a good all-season tire can pass the test. So do your homework before you buy.