December 14, 2013

Snow, Ice, and Your Tires

You know you're in trouble when it's been snowing, you're out on the road - and more than half of the other vehicles on the road are snow ploughs.

Photo by SPQRobin

Under those conditions the wisest thing to do is to stay at home. Build a snowman or an igloo with your children, bake bread, make some slow food, settle with a good book and a cup of hot chocolate while your children shovel the driveway. Enjoy the day. Take a vacation day if you have to. An employer that requires its employees to struggle their way into work under unsafe road conditions is not a good employer.

If you absolutely must go out into the great white world, remember that your tires are your best friends, more than they usually are.

If you live in a place where wintry conditions happen for several months of the year, you may consider getting winter tires: they are designed to give better traction than year-round tires, by the structure and depth of the treads. But more importanly, the material itself remains softer and more pliable at low temperatures, giving better traction even on dry (but cold) roads. This means better handling, and a shorter stopping distance. It's not surprising that winter tires are popular in Canada.

If you live in warmer climates you might not need winter tires. But these days, with climate change making weather more erratic everywhere, living in a temperate zone is not a guarantee that you will never be visited by snow. Even Jerusalem had enough snow to build good snowmen. That makes snow-covered palm trees the new image for Christmas cards.

Snow in Jerusalem. Via weather.com

Obviously, if it snows once in a blue moon where you live, you're not going to spring for winter tires. You don't have to. You don't even have to do anything special to your regular tires. But watch out for urban myths. In particular, there is a myth floating around that letting the air out of your tires gives you a safer ride on snow.

It is a myth.

Sure, soft tires give you better traction on snow and ice. If that's all you did, and at low speeds, and not very far, you may be allright. But consider also that the rubber is harder; under-inflating your tires causes a larger deformation to your tires which is tough on the hardened rubber. When you go driving at higher speeds, that larger deformation can cause the tires to heat up excessively, and you may end up with blown tires just when you least need it: on the side of a snowed-over highway, for instance.

The advice experts give is to check your tires before you drive away, and make sure they're inflated to the proper pressure while cold. If the roads are icy, you're not going that fast, and the tires don't warm up they way they usually do, so the pressure inside (which depends on the temperature) stays lower than usual, keeping the tires softer. This way, if the highway is clear when you make it there, and you go at higher speeds, the tires will warm up in a safe way, at the proper pressure.

Speaking of speeds: your best friend on icy or snowy roads (apart from your properly inflated tires) is patience. The traction, or sideways force, you need to go around the corner depends quadratically on the speed at which you take that corner, so you need to slow to a crawl to take that corner without starting to slip and slide.

Making it up the hill is also best done at low speeds. If you have all-wheel drive, make sure it's turned on. AWD is very helpful for getting forward in deeper snow, and up hills. However, it is not helpful for steering per se. And the extra weight works against you in braking.

In fact, if you drive a car with AWD you would be well advised to be extra careful in snow: because the feeling of better traction on the wheels going forward may give you a false sense of security. The truth is that in wintry conditions, AWD does not give you better handling; Getting around the corners safely still requires care and slow speed. And you may need a significantly longer brake length.

In Sweden, the Volvo S60 is available in nine different versions. Only one of those nine has AWD. Because real Swedes don't need AWD to negotiate their snowy roads. But I bet they do winter tires.



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  1. I live in a part of the UK which regularly gets snow, we put winter tyres on our cars. I agree with what you said about employers who expect their employees to make it to work regardless of the conditions are not good employers. Sadly in the UK some parts experience snow sporadically and then go into panic when trying to deal with it. When you are used to it you just get on with, carefully and sensibly, driving in snow requires practice just like any other driving.

    1. I confess we have no winter tires: when it snows hard we simply stay at home, since usually schools are closed (and CelloDad telecommutes anyway). Our out-of-the-way street tends to be one of the last to get a visit from the snowplough. If we must go out, say for food, we can always take out the sled :-)

      I think, with climate change proceeding apace, there will be more places that get freak snowfall. Like Cairo and Jerusalem.


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