Vehicle tires that have metal pins or "studs" protruding from them are called studded tires. Since tires are made with different tread depths, their studs are varied in length. The studs usually consist of tungsten carbide pins encased inside of a cylindrical metal piece that is held in the tire by a flange. It is the pins that protrude from the tire and cut into road ice, and chip away at pavement. Typically, 60 to 120 studs are inserted into each tire’s tread.
Studded tires have been in existence in various forms since the end of the 19th century. Modern versions of the tires first became popular in Scandinavian countries to make it easier and safer to drive on snowy, icy roads. Starting in the 1960s, studded tires saw widespread use in the United States. It was thought that the tires made driving safer because of the way the metal pins in bit into the ice and caused enough friction to prevent slipping and sliding.
During the 1970s, research engineers staring looking at safety issues related to the use of such tires, as well as the damage they cause to pavement. As a result, studded tires underwent technical improvements during that decade, and on through the 1990s. Some states in the US have restricted the use of studded tires to the winter driving season or banned them entirely because of pavement damage and safety issues. Countries like Germany, Belgium, and Japan also have banned their use. In the case of Japan, tires with metal studs were banned in part because the dust from the damaged concrete caused noticeable air pollution along its highways during their winter months.
Studded tires can cause ruts in pavement when the studs chip into a road or highway’s surface, especially when a driver is going fast along the road or highway. This means that when it rains, there could be a hydroplaning hazard. Prior to the banning of studded tires in various countries and American states, citizens had to pay many millions in taxes each year to try to keep roads and highways in good, safe condition. The extent of damage that occurs from the use of studded tires depends on stud length, how much the studs weigh, the number of studs per tire, the type of pavement surface, and vehicle speed.