Snow tires are usually tires with a different rubber composition from all-weather tires. Cold-weather tires include a greater percentage of natural rubber and silica so there is not as much hardening as found in synthetic rubber in cold conditions:[2] they provide better traction at lower temperatures.
Snow tires provide more small-tread areas, increasing traction on snow and, in wet conditions, allowing water to escape from under the tire more easily. This reduces the risk of hydroplaning. In much of Scandinavia, snow tires have metal studs to improve grip on packed snow or ice, but such tires are prohibited in most other countries for the damage they cause to the road surface.[3] Snow tires do not eliminate skidding on ice and snow, but they greatly reduce the risk.
http://en.wikipedia.org/wiki/Snow_tires
