Knobby tire
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Knobby tires are tires that have a coarse tread with knobs that provide more traction on surfaces that are not paved.
[edit] Off-road use
Knobby tires are used mainly on off-road vehicles. They are the most common factory-installed tire on motocross bikes, ATVs, and mountain bikes. They may also be fitted as an aftermarket option on four wheel drive vehicles. Their versatility on many surfaces is one of the main reasons for their popularity.
Rubber knobs on the surface portion of the tire that comes in contact with the ground provide substantially more traction than street tires. In a manner similar to shoe cleats, the weight of the vehicle causes the knobs to dig into the surface. Knobby tires have chunky, deep treads for maximum grip on loose dirt, mud, sand, or gravel, but on paved surfaces, such tires tend to have less grip than street tires. Tires with less aggressive knobs (smaller knobs and the shape of the tread cross-section closer to that of street tires) can provide a compromise, giving less grip off-road, but a grip closer to that of street tires on paved surfaces. Such tires are useful for dual-sport motorcycles and other vehicles designed to be used both off-road and on pavement.
Because of the low tire pressure sometimes used with these tires, the tire has a chance of coming off the wheel, or the tire and wheel may slip against each other. To prevent this from happening, a beadlock or rim lock can be used to clamp the tire to the wheel.
[edit] Street use
Depending on the model of tire, a knobby tire may or may not be approved by the DOT. A knobby tire approved for street use is referred to as a "DOT knobby" or a "D.O.T. knobby." The markings on the sidewall of a DOT knobby include a DOT code (U.S.) with the last four digits representing the week and year the tire was built, which identifies the tire as street legal. If the knobby tire has markings like "Motocross Use Only" or "Not for Highway Use", then the tire is not street legal. Even if street legal, knobby tires are generally not suitable for long distances on roads or paved surfaces, because the pavement wears down the knobs and ruins the tires for off-road use.
[edit] See also
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