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So how exactly do winter tires work?

Technology

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28/10/2019

The current WinterContact TS 850 P tire from Continental is designed for mid-range models and above. Photo: Continental

 

Driver assistance and safety systems help prevent crashes. At VisionZeroWorld we explain how ABS, ESC and other safety-related technologies work. This time it’s the turn of winter tires.


Winter often arrives quite literally overnight. You open the blinds and there’s a blanket of white covering the world outside. Kids love it. But grown-ups have been heard to groan, particularly if they’re facing a commute by car. Not just because they have to scrape the ice off the windows. Often enough it’s because they’ve forgotten to get their winter tires fitted. And that can have unpleasant consequences. The fact is that the rubber compounds in summer tires are not designed to deal with icy conditions. They become less and less supple as the temperature drops. As a result, the tires rapidly lose their grip in the winter, cars tend to skid on cornering and braking distances get much longer, even on dry roads. Under these conditions, even driver assistance systems like ABS and ESP aren’t much help and are often completely ineffectual. Winter tires can prevent these problems arising. At Continental, the latest models are the WinterContact TS 860 for compact to mid-range vehicles, the WinterContact TS 850 P for mid-range models and above, and the WinterContact TS 860 S for sports cars and luxury limousines.

 

But what is it about winter tires that makes them work? The answer lies in the material that they are made of. The main component of any tire is rubber. The proportion of natural rubber, obtained from rubber trees, is higher in winter tire compounds than in summer tires. The proportion of man-made synthetic rubber, by contrast, is lower in winter tires. This way, the tires remain supple and flexible even at low temperatures, helping them to stay firmly in touch with the road. That’s because natural rubber is much more flexible than synthetic rubber at temperatures around freezing point. But tire manufacturers like Continental also traditionally put their faith in other ingredients, such as the fillers that reinforce the bonding of the rubber compound. For many years the first-choice filler was carbon black. That’s why tires are black. In the meantime, however, tire manufacturers are switching to silica. This particular filler can boost the abrasion resistance of winter tires and at the same time help them deliver more mileage.

 

But it’s not just the material in winter tires that makes the difference; the tread too offers decisive advantages in terms of functionality. The purpose-carved grooves in each tire are cut in specific directions to ensure that snow and slush are dispersed to the outsides of the tire and that there is no build-up of material ahead of the tire. And when snow is falling, the small, fine incisions in the tread also have a key role to play. These are the sipes and they are the most important component of the tread architecture. In bad weather, as pressure comes to bear on these narrow recesses they act like little crampons that hook themselves into the ground, delivering the grip that makes all the difference when accelerating and braking in the wet and on snow.

When snow falls, the sipes that are created in winter tires by molds like these act like little crampons and hook themselves into the ground, providing the car with more grip. Photo: Continental

 

In Continental’s latest generation of winter tires, these capabilities are complemented by three technical innovations: While Liquid Layer Drainage cuts braking distances on icy roads thanks to an additional drainage channel in the tread, SnowCurve+ technology, with an additional groove in the wall of the tread blocks, provides more effective interlocking with the snow and in particular makes for safe cornering on snow-covered roads. At the same time, the tires’ innovative Cool Chili compound includes a high proportion of silica which, due to its special damping characteristics, delivers a decisive reduction in braking distances, especially in the wet.

 

You need to remember, of course, that even winter tires can’t work wonders. They may ensure better grip on snow and in cold weather, but even with winter tires fitted, braking distances on snow are still longer. To get the best out of your winter tires, you should keep a regular check on tire pressures. Not enough pressure and the tires will be unable to perform to their full high-tech potential. So when is the right time to fit winter tires? It depends, of course, on where you live and drive, but the German rule of thumb is to use winter tires from October to Easter (in German “from O to O”, as Easter = Ostern). But the experts reckon that the time is right when the thermometer drops below 7°C, which is roughly 45°F.