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Snow chains, or tire chains, are devices fitted to the tires of vehicles to provide increased traction when driving through snow and ice.
Snow chains attach to the drive wheels of a vehicle or special systems deploy chains which swing under the tires automatically. Although named after steel chain, snow chains may be made of other materials and in a variety of patterns and strengths. Chains are usually sold in pairs and often must be purchased to match a particular tire size (tire diameter and tread width), although some designs can be adjusted to fit various sizes of tire. Driving with chains reduces fuel efficiency, and can reduce the allowable speed of the automobile to approximately 50 km/h (30 mph), but increase traction and braking on snowy or icy surfaces. Some regions require chains to be used under some weather conditions, but other areas prohibit the use of chains, as they can damage road surfaces.
Snow chains were invented in 1904 by Harry D. Weed in Canastota, New York. Weed received U.S. patent 0,768,495 for his "Grip-Tread for Pneumatic Tires" on August 23, 1904. Weed's great-grandson, James Weed, said that Harry got the idea of creating chains for tires when he saw drivers wrap rope, or even vines, around their tires to increase traction on muddy or snowy roads. At this time, most people in rural Northern regions wouldn't bother driving automobiles in the winter at all, since roads were usually rolled for use with horse-drawn sleighs, rather than plowed. Automobiles were generally not winter vehicles, for a variety of reasons until the 1930s or 1940s in some areas. Only in urban areas was it possible to remove snow from streets. He sought to make a traction device that was more durable and would work with snow as well as mud.
In January 1923, American inventor Oscar E. Brown obtained U.S. patent 1,440,580 for his “Nonskid Attachment for Vehicle Tires”.
In July 1935, the Canadian Auguste Trudeau obtained a patent for his tread and anti-skidding chain.
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.
In case of running wheel loaders, it is recommended to use special protection chains due to intense pressure on tires during work.
Tires come with standardized tire code sizing information, found on the sidewalls of the tires. The first letter(s), indicate the vehicle type (P for passenger, LT for light truck). The next three digits indicate the tire's width in millimeters. The middle two digit number indicates the tire's height-to-width ratio. The next character is a letter "R", which indicates radial ply tires (rather than radius). followed by a final two digit number indicating the rim size for the vehicle's wheels.
Additionally, the correct Society of Automotive Engineers (SAE) class of snow chains must be installed, based on the wheel clearance of the vehicle.
The SAE Class "S" well clearance is a common requirement on newer cars, especially if after-market wider, low-profile, or larger tires and/or wheels are fitted.
The classes are defined as follows:
SAE Class S: Regular (non-reinforced) passenger tire traction devices for vehicles with restricted wheel well clearance.
SAE Class U: Regular (non-reinforced) and lug-reinforced passenger tire traction devices for vehicles with regular (non-restricted) wheel well clearances.
SAE Class W: Passenger tire traction devices that use light truck components, as well as some light truck traction devices.
