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driving concerns

2012 Jeep Wrangler Unlimited Arctic

I'm thinking of buying a new SUV. While I don't intend to take it off road, I want one that has good traction in deep snow. I'm considering four-wheel-drive, but I'm wondering if all-wheel-drive would be just as good. If both are equipped with snow tires, is one significantly better than the other in snow?

– Glenn, St. John's

Four-wheel-drive might be better at getting your SUV unstuck from waist-deep snow on, say, a private road that has never seen a snow plow – but all-wheel-drive (AWD) is better for general winter driving because it decides when you need those extra two wheels, says the Canada Safety Council.

"For the average driver, AWD is better – It automatically kicks in as needed," says Raynald Marchand, CSC general manager of programs, in an email. "4WD has to be manually selected, and it's useful for drivers who will be off-roading."

I didn't find any tests comparing AWD and 4WD drive vehicles in deep snow. So I asked some manufacturers who produce both kinds of vehicles.

Figuring out the difference between the two involves trudging through marketing because, these days, car makers use the terms interchangeably. And some have systems that they say combine the benefits of the two. And there are higher-end systems that divide the power between the left and right wheels for better cornering.

Back in the olden days of 4WD (the '80s), vehicles were driven by two wheels until you turned on the 4WD.

"It was two wheels until you pushed something or pulled something," says Hayato Mori, manager of product planning for Honda Canada. "A lot of Jeeps had a low gear transfer and a high gear transfer."

In a traditional 4WD, the front and rear wheels lock together to get you moving if you're stuck.

How is AWD different? In modern AWD systems, there's no button to press – they're primarily front-wheel-drive. but the vehicle transfers power to the rear wheels when it senses that you're losing traction, Mori says. The driver doesn't have to turn anything on. With typical AWD, the wheels don't lock together.

"Hondas uses a pump system to engage the clutch to the rear wheels," Mori says. "As soon as slippage is detected to the front, the rear wheels get going.

AWD drive vehicles tend to be cheaper and they have better fuel economy, mostly because they're lighter, Mori says.

"As you get more heavy duty, it adds weight, it adds drag to the vehicle," he says. "Most consumers won't need a heavy-duty 4x4."

Some modern 4WD vehicles combine the two types, transferring torque to the rear automatically like an AWD, without the driver needing to do anything – but also allowing you to flip a switch to lock the centre differential when needed.

"Like if you get bogged down in snow," Mori says. "But it's only good for low speeds."

Generally, 4WD is unsafe to use on asphalt – the locking wheels tend to plow straight through corners, the CSC says.

"In general, 4WD systems are only for use on surfaces with low traction,' wrote Tim Franklin, Nissan Canada's product planning manager, in an email. "An AWD system is typically designed so that it can be operated on all road surfaces."

Franklin says AWD is probably best "for the casual driver who doesn't plan on a winter expedition across Labrador."

Both 4WD and AWD just help you get going in slippery conditions, but they don't improve handling on corners and they don't improve braking distances. Both can give drivers a false sense of security.

"Once it starts driving, unless you have snow tires, all you have is a heavy car," Mori says. "At the end of the day, you can't beat physics."

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