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 will reduce fuel efficiency and can limit the speed of the automobile to approximately 50 km/h (30 mph).
In snowy conditions, transportation authorities may require snow chains to be fitted on vehicles. This can apply to all vehicles, or those that lack certain motive combinations such as four-wheel drive and/or specific classifications of tires. Local requirements may be enforced at checkpoints. Snow chains should always be fitted to one or more drive axles of a vehicle, with varying requirements 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' being required to have snow chains
fitted when conditions and/or signage require it.