Snow chains, or tire chains, are devices fitted to the tires of vehicles to provide maximum traction when driving through snow and ice.
Snow chains are attached to the drive wheels of a vehicle. Chains are usually sold in pairs and must be purchased to match a particular tire size (tire diameter and tread width). Driving with chains reduces fuel efficiency and can reduce the speed of the automobile to approximately 30 mph (50 km/h).In snowy conditions, transportation authorities may require that snow chains or other traction aids be installed on vehicles, or at least supplied for them. This can apply to all vehicles, or only those without other traction aids, such as four-wheel drive or special tires. Local requirements may be enforced at checkpoints or by other type of inspection. Snow chains should be installed on one or more drive axles of the vehicle, with requirements varying for dual-tire or multi-driven-axle vehicles that range from 'one pair of tires on a driven axle' to 'all tires on all driven axles', possibly also one or both steering (front) wheels, requiring snow chains whenever required by signage or conditions.