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Snow studded tires are tires that have small metal protrusions called studs all over them. The studs increase traction in dangerous snow and ice. In order to be effective, snow studded tires must be used on all wheels of the vehicle. Although they improve traction on snow and ice, research shows that cars equipped with studded tires often have longer braking distances and reduced traction on pavement when compared to those with regular tires. Due to their tendency to cause significant pavement damage, however, snow studded tire use is restricted to the winter season in areas that still allow them.
The snow and ice conditions common in many parts of the world cause significant difficulties for motorists. Vehicles being driven on these surfaces tend to skid and slip due to the lack of traction and slick conditions, and many cars not be able to move at all. In areas where hazardous winter driving is a common problem, many drivers rely on traction devices such as snow studded tires or chains so that they may reach their destinations safely.
Approximately 60 to 120 studs are used on snow studded tires that are made of an extremely hard durable metal called tungsten carbide. The studs consist of two parts. The outer part is a hollow outer sleeve or jacket that gets imbedded into the tire and protrudes approximately 0.05 inches (1.5 mm) from the surface. The inner portion is a tungsten carbide pin that is inserted into the stud jacket. This two-part construction allows a stud to maintain a constant level as the tire gets worn down.
To obtain the benefit of snow studded tires, they must be installed on all four wheels of the vehicle. They improve traction on snowy or icy surfaces by increasing the friction between the tire and the road. The studs dig into the the ice or snow and prevent a car from slipping. This is similar to the way cleats give some athletes improved traction on grassy fields. The use of now studded tires is often reserved for areas with frequent winter driving hazards, however, because the tires are less effective on wet or dry pavement than standard tires. They also generate increased road noise and a slightly bumpier ride.
The ability to dig into surfaces that can make snow studded tires so useful in slick conditions is also a problem on bare pavement. Studded tires cause significant pitting and ruts in the pavement where they are frequently used. This damage can cost local authorities enormous sums of money to repair; as a result, the use of studded tires is often restricted to the winter months. They are also against the law in some countries.