Way back when, before the four-wheel-drive craze, before the advent of traction control systems, and even before all-season radials, most drivers north of the Mason-Dixon Line performed a hallowed annual ritual--installing snow tires on their cars. In fact, snow tires once ranked right alongside leftover turkey and holiday shopping as a day-after-Thanksgiving tradition.

Old ways die hard. Today, many experts still insist that snow tires represent the single best investment you can make for wintertime traction--dollar for dollar, better than four-wheel drive, all-wheel drive or high-tech traction control.

"Tires play the single largest role in determining how your vehicle will handle in an emergency situation," says Bob Toth of Goodyear. "It doesn't matter how many electronic systems you have in your vehicle. The brakes stop the wheels; the tires stop the vehicle."

As good as they are on snow and ice, however, snow tires have some drawbacks on dry pavement. When considering snow tires, drivers face a basic cost-benefit analysis. Do the advantages of snow tires in slippery conditions outweigh their disadvantages on dry winter pavement? Is extra traction worth the extra hassle and expense?

The Real Deal
To begin to answer those questions intelligently, you have to understand the difference between all-season radials and real, honest-to-goodness snow tires. Most people believe that all-season radials carrying the "M+S" rating on the sidewall (for "mud and snow") equal snow tires. They're wrong.

Most localities require motorists to have "winter tires" during heavy snowfalls or risk a ticket, and M+S tires meet those requirements. But that makes them snow tires only in the street-legal sense, not in practice.

"Like most tires, all-season radials are a compromise," explains Dan Zielinski of the Rubber Manufacturers Association (RMA), the industry group that promulgates these voluntary standards. "They're designed to give adequate performance for a preponderance of seasonal conditions."

In fact, to earn an M+S rating, tires need only have a particular type of tread pattern--for example, one in which slots and grooves make up at least 25 percent of the footprint. They need not pass any performance test.

True snow tires, on the other hand, carry RMA's so-called "mountain/snowflake" symbol--and must pass a more stringent performance-based traction test to earn it. To meet those performance requirements, snow tires have much different tread designs and different compositions than all-season M+S tires. They boast more of what engineers call "sipes"--molded grooves in the rubber that act as blades to bite into snow, slush and ice. Their rubber compounds also stay softer and more flexible in sub-freezing temperatures, which provides a better grip.

But as tires built for a specific purpose, true snow tires also feel noticeably different than all-season radials under normal, nonsnowy conditions. Their softer rubber and deep, chunky treads give your vehicle rather squirmy handling on dry roads. The tread depth also makes them noisier on bare pavement. And they wear much faster than conventional radials.

Furthermore, "snow tires are likely to build up heat at constant highway speeds," notes RMA's Zielinski. "And because heat is a tire's greatest enemy, you might be setting yourself up for tire failure in warmer weather." For all those reasons, you have to replace snow tires with regular tires come spring.

Weighing Your Options
Given snow tires' unquestionably superior winter traction, set off against their added expense and hassle, degraded handling characteristics and faster wear on plain pavement, should you install them? That depends entirely on where and how you drive.

"Most people in this area do 95 percent of their winter driving on plowed roads," says Frank Niland of the Club's Traffic Safety Department. "For them, all-season radials work just fine, and they don't need snow tires."

But then there are special circumstances. What if you head into the mountains a few times a month to ski? What if your home has a long, steep gravel driveway that always has a layer of packed snow, even after plowing? What if your work schedule regularly forces you to beat road crews onto the highway for your daily commute? Then you might value the extra margin of safety provided by snow tires in the worst conditions.

Two vs. Four
For some people, this winter-traction calculus becomes way too complicated, and they simply decide to split the difference. They install a pair of snow tires on one axle and leave a pair of all-season radials on the other. Then the question becomes, which axle deserves the extra traction?

Even within the tire industry, experts argue endlessly about the answer. Some insist that, if you must use only two snow tires, they should go on the drive axle; others counter that they should always go on the rear, regardless of the drivetrain. Either choice presents problems, so the argument really hinges on the lesser of two evils. Putting the higher-traction tires on the front axle (in a front-wheel-drive car, for instance) increases the risk of a rear-wheel skid, which everyone agrees is far more difficult to control than a front-wheel skid. "But if you put them on the rear, you're assuming that it's more important to get started than it is to stop," notes Goodyear's Toth. "And everyone knows that the front wheels do most of the work during braking. In that case, they need the best traction."

Toth insists that four snow tires beat two any day. "Putting the same tires on all four corners delivers the best balance of handling, as well as the best traction for starting and stopping," he says. "Snow tires represent such a radical difference in traction that you'll notice the difference in handling if you use only two, no matter where you put them."

Besides, when you consider that you're using snow tires for the extra safety margin they provide at a relatively low cost, investing in a complete set of four makes perfect sense.