Cars

The old debate: All-wheel-drive vs. winter tires

LOW-TEMP TIRES: Note the wide grooves and even the micro-grooves on these winter tires, designed for dispersing snow and slush.
LOW-TEMP TIRES: Note the wide grooves and even the micro-grooves on these winter tires, designed for dispersing snow and slush.Credit: PHOTO: TIRERACK.COM

Many readers have asked about the benefits of all-wheel drive and wonder if their cars would perform even better with dedicated snow tires. This is especially true for Subaru owners, who tout the all-wheel capabilities of their chariots. We all know that Subarus are nearly as ubiquitous as Dunkin’ Donuts in New England, but as good as they are, their superior AWD is not a magic bullet. Far more goes into getting you through the snow, and a poor set of tires can render even the most advanced all-wheel-drive system ineffective.

You hear a lot about all-wheel-drive in ads, but there is far less mention of tire styles. To get a keener sense of the part a good tire plays, we spoke with Sarah Robinson of Michelin tires.

“Of course, I’m biased toward tires,” says Robinson, “but the difference between a typical all-season tire and a purposeful winter tire is astronomical. All-season tire tech is improving, but there is no replacement for the chemical compound and tread pattern of winter tires.”

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Summer tires work on warmth. When they heat up, the rubber becomes sticky. This is how a sports car can grip its way around a track. When the temperature drops, the rubber in these summer tires harden. Winter tires use a softer compound that does not require the same level of heat to develop grip. Winter tires also have a tread pattern that is designed to take snow and disperse it as much as possible. Snow sticks to snow, just ask your kids after they’ve pelted each other with 2,500 snowballs. If you can keep the snow away from the rubber, you’re half way there—but all-season tires only go so far.

“Any time you are in a climate where temperatures are constantly under 40 degrees,” Robinson continues, “all-seasons are under their traction capabilities. As the temperature drops below the 35 to 40 degree mark, grip declines, cornering drops, and braking drops.”

Since the second half of the 20th century, automakers have advertised the winter-driving benefits of front-wheel-drive cars. Rear-wheel-drive uses the power from the rear to put pressure onto the front wheels that are steering. With front-wheel-drive cars, the wheels that steer are also the wheels with the power. There was some advantage to FWD over RWD, but the switch also made for more economical packaging, hence the push from automakers. As all-wheel-drive vehicles were introduced, their all-weather capabilities became quite apparent. Variations have been around for decades, but the true standard-bearers have been Audi and Subaru. Audi touts its Quattro AWD system while Subaru promotes symmetrical all-wheel-drive.

If you’re shopping for a vehicle, and notice that there is the option for either a front-wheel-drive or all-wheel-drive, odds are that the AWD system is front-wheel biased. That means that it spends most of its time powering the front wheels, engaging the rear wheels when there is slippage. In many winter driving conditions, by the time the rear wheels engage, it’s already too late.

Regardless of what AWD you choose, it is better than front-wheel-drive, and in many cases, better than four-wheel-drive. When engaged, four –wheel-drive claws away well, but you have to choose when to engage four-wheel-drive. Leaving 4WD engaged all the time hurts the transfer case gears, especially if operating at speeds over 40 mph. Because of that, those driving SUVs or trucks have to wait until four-wheel-drive is absolutely needed. So—like a race team deciding when to switch to wet tires—there is a great deal of choice about when to make the call.

If you have a rear-wheel-drive vehicle, we would highly recommend a dedicated set of winter tires. Front-wheel-drive vehicles with all-seasons will get by, but there will be days when you won’t be able to make it to the end of your street. All-wheel-drive vehicles will make it through the snow with all-season tires, but driving an AWD car with dedicated snow tires is the safest choice.

Still, not every driver will commit to winter tires. The downside of such a specific choice is that you now have to purchase (and eventually replace) two sets of wheels and tires. Once again, Robinson, is quite familiar with this issue:

“Going for summer AND winter tires can be a significant upfront investment,” says Robinson, “but if you do it right, you’re going to get several seasons out of those tires. The wear rate is very low. You can get 4 to 6 years out of those years before the warranty runs out.”

When you notice a vehicle in the winter that looks like it is driving on four spare wheels, they are typically driving on winter tires, with a dedicated set of steel wheels. “Most people will go out and buy a set of beater wheels,” says Robinson. “That helps keep costs down. And when you match the costs of owning winters and summers against the value of safety—safety will always win out.”

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