The warmth of friction generated by a tire spinning on snow creates a microscopic layer of water that lubricates the space between tires and road surface. Part of the problem is that a car's immense weight is supported by just a few square inches where each tire meets the ground. Putting all of that energy in a small area, you generate an awful lot of melt-water, Colbeck said. Skis, snowboards and ice skates are fun because they glide on this microscopic film of water. When Tommy Moe is downhill racing, each of his ski bottoms are putting out as much heat as three 100-watt light bulbs, Colbeck said.
Roads are less slippery when it's cold.
At 40 below, for example, our main concern is making it to an intersection rather than sliding through it. When it's that cold, we don't slide as much because the heat generated by tires is quickly absorbed the by the frigid air. Cold snow becomes slicker, though, when it's packed down. Packed snow has less friction than unpacked snow. After a few cars drive over deep snow, the tires polish the surface, changing the snow's texture from spiky to glassy.