A wheel chain is a device that helps to give a vehicle traction on snowy winter roads. The wheel chain, or snow chain as it is commonly called, is actually a pair of chains linked by shorter chains that entirely encompass a tire. When the wheel chain is placed around a tire and fastened, the vehicle is able to move easily through snow-covered roadways albeit at a much slower speed.
In many western United States areas, a wheel chain is required by law to carried by any vehicle traveling the roadways during storms in the winter months. Areas such as the Rocky Mountains are subject to very heavy snowfall without notice and vehicles can become stranded on the snow covered roads. The wheel chain is easily attached to the vehicle's drive tires and digs through the snow and ice to provide traction. Due to the bumpy ride as the chains dig through the snow, the vehicle is operated at greatly reduced speeds to prevent damage to both the vehicle and the road's surface.
Variations of the wheel chain such as cable type traction aids and plastic belt-like devices have been tried with some small level of success, but the wheel chain remains the undisputed best of traction-aiding devices in most cases. When properly applied, the wheel chain is not tight on the drive tire. The chain remains somewhat loose, allowing it to sling snow and ice as the tire digs forward through the snow. This also helps to keep the tire's treads free of snow to aid in the traction of the vehicle.
Vehicles such as semi trucks that incorporate a dual drive tire system require two wheel chains per drive wheel assembly. This can call for as many as four to eight wheel chains per truck. Some truck drivers choose to apply wheel chains to only one axle unless the roads are severely covered. On vehicles such as four-wheel drive pick-up trucks, some drivers place wheel chains on all four corners of the vehicle.
While the wheel chain aids in forward bite to assist a vehicle in moving through inclement weather, it also aids in braking. The chains dig into the roadway chewing through packed snow and ice to help slow the vehicle down. It can be necessary to pump the brakes, allowing the tires to turn in the event of snow building up under the chains. A slight rotation will place a clean chain on the roadway, allowing the tire to gain traction once again.