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Winter tires are best when you’re driving through snow, or in temperatures below 7 degrees Celsius.

My mom drives keeps her winter tires on all year. She says if they work in the winter, they should work fine all year. Can you tell her she's wrong? Since she doesn't want to change tires, I think she should just keep all seasons on all year. I worry that she's ruined her winter tires by using them in the summer and that she'll slide through intersections now that it's freezing again. Should I be worried?

– Shawn, Saskatoon

Our summers are short in Canada, but not that short.

If you keep winter tires on 12 months a year, you'll not only have to replace them sooner, but you could be risking your car's ability to stop in the spring, summer and fall, experts say.

"What makes them grip so well in winter is their formulated trade compound which stays soft in the cold," says Gene Petersen, tire program leader at Consumer Reports magazine. "Normally you should get 2-3 seasons out of winter tires – but if you use them all year long, winter tires generally don't handle as well as all-season tires and wear out faster."

Whether or not your mom's winter tires are safe for this winter will depend on how much tread depth they have left – but Consumer Reports say their tests show winter tires are potentially worse at stopping on dry and wet summer roads.

In the magazine's comparison tests of 2012 tires on a Chevy Cruze, it took winter tires about 24 feet (7 metres) further, on average, to stop compared to all-season tires when travelling at 60 mph (96.5 km/h) on a dry track in normal temperatures.

During the same test on a track sprayed with a thin layer of water, winter tires took about 31 feet further to stop.

"That's one and a half, two car lengths longer," Petersen said. "That could be the difference between avoiding an accident or not."

When braking on ice from 10 mph (16 km/h), winter tires stopped at least 7 feet (2 metres) shorter, on average, than all-season tires. The best winter tire stopped about 15 feet (4.5 metres) shorter than the average all-season tire.

Winter tires were also better at accelerating through snow – they measured the distance it took the test car to accelerate from 5-20 mph (16-32 km/h) on moderately packed snow, like what you'd get on a well-travelled winter road.

"Winter tires took an average of 19 feet (6 metres) less than all-season tires, so in other words the average of all winter tires was about 80 feet and it took all-season tires 99 feet" Petersen said. "So winter tires don't only get you out of snow, they can get you going faster."

Then again, this is just one set of tests. There was a controversy in Quebec – where, by law, winter tires are required on all cars between Dec. 15 and March 15 – over whether winter tires were less safe than all seasons on summer roads. A study by the Quebec Provincial Police showed no significant difference, says the Canada Safety Council "The difference was marginal," says Raynald Marchand, general manager of the Canada Safety Council.

The bigger question this time of year is whether you should keep on all seasons or switch to winter tires.

The Canada Safety Council and the Automobile Protection Association both recommend switching to winter tires (tires with the mountain snow flake label on the side) when the temperature drops.

"The difficulty with all-season tires is: at about 7C, an all season tire's rubber compound starts to lose traction," says Marchand.

The rubber in all-season tires gets hard – think of a hockey puck – as it gets cold. The rubber in winter tires is designed to stay supple to –40C If you live somewhere in Canada without much snow (it's a short list), or if you're only driving occasionally on well-plowed roads – you might be able to get by with keeping all seasons on all year.

"Winter tires excel in snow but in my experience you give up dry road grip and precision," says Mac Demere, a freelance automotive writer. "The closest I've lived to Canada was Denver, and they were mostly pretty good at getting roads plowed. But I skied then, so I put on winter tires," he says.

"It really depends on where and how you drive."

Demere, a former race car driver who did road tests for Michelin and Car and Driver magazine, says tires are tied with brakes as the most important safety device on your car – they're not something to skimp on. "Buying high quality tires is basically buying cheap insurance. It's a lot easier to avoid a crash than it is to survive one," he says.

You need to have four winter tires, not just two, and Demere recommends having a dedicated set of wheels for winter tires.

Whichever tires you choose, they need to be kept at the correct tire pressure for your vehicle. That's not the number on the side of the tire, which is the maximum the tires can hold.

Instead, look in the manual – if it's not there it will be on a sticker somewhere on the vehicle, usually on the pillar next to the driver's-side door, Marchand says.

"In the winter, it's important to add air to get the correct tire pressure," says Marchand. "Even if you have nitrogen in the tires, add regular air."

How long will tires last? It depends on where and how you drive them, Marchand says.

"In Canada, provincial and federal regulations say tires have to have at least a 2 mm tread depth," says Marchand.

The APA recommends checking wear by sticking a quarter in the trench between the treads.

New winter tires are between 10/32 and 13/32 inches (8mm – 1cm) deep – if the tire covers the caribou's nose, it means you still have at least 6/32 – 5/32 of an inch (4-5 mm) of tread left and the tires will probably last for another 10,000 km, the APA says.

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