What are half a dozen BMWs and Porsches doing inside a hockey rink in South Bend, Indiana? They're trying to convince a group of editors and writers that snow tires make a difference. And given the unpredictable variety of the 2006-2007 winter, that's one place you can always find icy conditions underfoot.

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Half of all advances in automotive performance in our lifetime have come from improvement in tires. So I've heard the tiremakers say. It may be true. One thing I now know to be true: The technology in snow tires is simply dazzling. If you live in snow country, you shouldn't be without them. Assuming, of course, it snows in snow country, something that hasn't happened universally this season, whether because of El Nino, global warming, the Almighty's unhappiness with skimpy clothes in public schools, or simply statistical variability.

Test-driving three BMW 325i's and three Porsche Cayennes back-to-back with regular tires, all-season tires, and snow tires showed me that tires make a huge difference in traction, stopping, and turning, with snow tires being by far the best. Conversely, winter tires really hold down performance in warm or just dry weather. Worse, a car with only two snow tires can be even more squirrelly.

The tests were set up by Tire Rack, a South Bend–based direct seller of tires and wheels, which has an admitted self-interest in getting you to buy more tires and wheels.

Having the test course indoors allowed for acceleration runs (brief ones), braking, and turns on simulated glare-ice conditions, something a hockey rink allows for quite well. First I tried a rear-drive BMW 325i with street tires and, no surprise, it took its time accelerating. And then, with the end of the rink looming, to stop. Carving an arc through cones, it was easy to slide across the cones except at the slowest speed. No one yet has crashed through the dasherboards, but it's possible to come close, and a lot of course-marker cones went flying. (Actually, the cones went briskly sliding, given the maximum 20-mph speed you can attain on a 200-by-85-foot rink.)

Then I switched to the Bimmer with all-season tires—all-season meaning the tire compound is a bit softer (stickier), and the tread is slightly more aggressive to grip in snow. The BMW lit off more quickly, stopped more quickly, and cornered at higher speeds. Then came the snow tires with even softer compounds and more aggressive tread, and they were wondrous: Accelerating, braking, and cornering on the ice rink felt as if there was bare asphalt underneath. Well, almost.

Switching to the three Porsche Cayennes, the differences in acceleration were a bit less pronounced, because the Cayenne is all-wheel-drive, while the 3 Series BMW is rear-drive. Comparing Porsche summer tires to BMW summer, all-season to all-season, and snow to snow, the Porsche got to speed faster despite its 5,000-plus pounds of bulk because of the all-wheel-drive. To eliminate variables, just one tire brand was used (Bridgestone) on all six vehicles. However, the Porsche's summer tire wasn't as summery as the BMW's. Braking, however, was little different between BMW and Porsche, meaning the BMW's rubber compound was optimized for better grip and sporty driving in summer, to the detriment of winter driving. Braking, however, was little different between BMW and Porsche, because on both cars all four wheels do the stopping.

Not many tire dealers have a test track in front of their buildings; but then, not many tire dealer buildings are 1 million square feet either. Tire Rack uses its track both to test tires and to run local editions of the Street Survival School, a safe-driving program for teen drivers that it co-sponsors nationwide.

Outdoors, we drove a set of BMWs with four configurations: summer tires, all-season tires, snow tires, and a mismatched combination of two summer tires in front and two snow tires in back. Not surprisingly, our times through a slalom course were best with summer tires. Perhaps surprising was how squirrelly (unsettled) the car felt with mismatched sets, notably worse than the car with all-snows. It was easy to spin the BMW or at least lose control when running the slalom cones and lane-changing at speed.

While there's not much call for slaloms on city streets, an emergency lane change happens to everyone, and the mismatched snow-and-summer tires could unsettle the car enough to put you in a spin that your car's stability control might not be able to prevent. In practical terms, the difference between 30 mph and 40 mph in a slalom or lane change was huge with the snow tires or mixed-set tires, but there was hardly any difference with the summer tires.

Tire Rack's VP Matt Edmonds says ice-traction equivalents ranged from 60 to 79 to 100 (100 being an arbitrary number) for the tested passenger-car summer, all-season, and snow tires, respectively. For the SUV (similar numbers would apply to an all-wheel drive light truck), the numbers are 72, 86, and 100. In rough terms, if it takes you 10 seconds to accelerate to a reasonable speed on a snowy or icy highway on ramp with good snow tires on the BMW, it would take you about 13 seconds with all-season tires, and 17 seconds with summer tires. Or 2 seconds for a snow-tire car to accelerate through an icy intersection with oncoming traffic bearing down versus 2.5 and 3.3 seconds. That could be the difference between safely clearing the intersection and learning just how quickly side airbags inflate. The wider range of passenger-car traction capabilities lay in part with the choice of a high-performance summer tire (aptly called Bridgestone's Pole Position) that was not intended for winter use.

Having finished second among the journalists present in informally timed runs, which was probably more a poor reflection on them than a positive for me, I'm now a semi-expert (in the land of the blind…). Here's what I'd suggest for your car or SUV.

If you live in a state that gets any snow, and you're buying just one set of tires, make them all-season tires. That's what a lot of passenger cars and SUVs come with already. If you live in snow country (or what would be snow country in normal years), get a set of snow tires, too: four of them. You'll have to decide for yourself what to do if you live in a marginal area where it snows some but not a lot.

If you have a sporty car with a handling, performance, or sport package, you probably have not just summer tires but performance-oriented summer tires, and their traction and braking is especially poor in winter (because the rubber compound gets hard in sub-freezing weather). So you really need a second set of tires and wheels for winter driving, and it's up to you to decide if they're snows or all-seasons. If your car has low-profile tires (60 or 50 series), go with a wheel 1 inch smaller and a higher-profile tire (60 or 70 series). In plain English, if you have 18-inch wheels for your current tires, mount snow tires on 17-inch wheels with taller sidewalls so the overall diameter is the same.

If you recall snow tires from a decade ago, forget what you remember. The technology is dramatically different and better. They all look black, but inside they're vastly different. Few if any drivers stud their snow tires anymore, both because the snow-tire compounds are so much better now, and because of how much the studs affect handling on dry roads, not to mention the way they chew up the asphalt.

Snow tires are typically mounted on steel wheels, not aluminum-alloy, but the differences are minimal now: Steel wheels may weigh only a pound or two more than alloys, and passable quality alloy wheels from China aren't much more costly than steel wheels. It may come down to cosmetics: Most steel wheels for snow tires are black.

Get four snow tires or none, but not two. That's especially so with front-drive cars, because for traction you'd want the snow tires in front, but for braking you don't want the rear tires to have less grip, and snow tires have more grip in snow—otherwise you risk the back end sliding around to become the front.

We put new tires on our cars recently. Did I practice Tire Rack's advice?

Halfway. We live in the New York City area, a far cry from the Great Lakes snow belt where we grew up, so I put four new all-season tires on our minivan (actually five, after an incident where the curb suddenly jumped out at the van and gashed the sidewall), and performance tires on my sport sedan—which I leave in the garage if it snows really hard. Anyway, when I go into the office, my commuter vehicle rides like it's on rails, because it is on rails. If need be, I can walk to the train station, assuming the trains themselves are running: Road-hugging weight isn't all it's cracked up to be. But today's snow tires are.