Off-road tire

Knobby tire on a 2008 Motovert pit bike.

Different treads on knobby mountain bike tires

Off-road tires (Off-road tyre) are a category of vehicle tires that use deep tread to provide more traction on unpaved surfaces such as loose dirt, mud, sand, or gravel. Compared to ice or snow tires, they lack studs but contain deeper and wider grooves meant to help the tread sink into mud or gravel surfaces.

Design

Off-road tires are typically radials with thick, deep tread. On dirt surfaces, the exposed edges of the tread dig into soft ground to give more traction than rolling friction alone, analogous to the traction provided by cleated shoes. These off-road tires provide their maximum grip on loose surfaces, but on paved surfaces the smaller contact patch affords less traction as compared to 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 enduro and dual-sport motorcycles and other vehicles designed to be used both off-road and on pavement.

Some off-road tires are designed to be used with low inflation pressure on difficult terrain, reducing their rigidity and allowing the tread to better conform to the terrain. Such a design may allow for use on a wider range of surfaces, but tubeless tires running under rated pressure run the risk of breaking their bead. A beadlock can be used to prevent this.

Off-Road tires specifications

Off-road tires feature slightly different specifications, than the wheels for the regular vehicles. The first digit in the tire size stands for the outer tire diameter (in inches). The second number of the tire size measurement is the width of tire (inches). The 3rd number of the off-road tire code reading is the same as in the regular automobile tires and identifies the inner diameter of the tire.

Not every owner of an off-road vehicle knows, what is the outer tire size of the tires they use, and it may be somewhat inconvenient to measure it at a spot.Though, knowing the standard tire size, one may easily calculate the outer diameter with the help of formula. It is important to note, however, that this formula is calculated in millimeters, not inches. As an example, let us consider the standard wheel size being 245/75-16.

• In the 245/75-16 wheels, the “245” denotes, that the width of the tire is 245 mm;
• The “75” means that the sidewall height is 75% of the tire width (245 mm);
• Sidewall height in mm: 245 mm x 75% = 183.75 mm;
• Conversion of the sidewall height from mm to inches: (183.75 mm x 2)/25.4 = 14.47 inches;
• Height of the side wall in niches has to be added to the wheel diameter in inches (in the example 245/75-16 it is 16): 14.47+16=30.47

If an owner decides to replace the factory tires will the off-road ones, it is important to consider not only the measurements, but the material and off-road wheel thread specs. Off-road tires are made of way softer rubber with wide and deep treads. Such tires do their job off-road and when travelling over rocky or muddy paths, but they wear fast when used on highways. Besides, off-road tires do not provide that maneuverable cornering, especially at speeds.

Use on bicycles, motorcycles, and quads

Off-road cycle tires, colloquially called knobbies, may be found on motocross and enduro motorcycles, ATVs, and mountain bikes. Tires for single-track vehicles and ATVs have a curved profile such that some tread only contacts the ground during turning.

Depending on the model of tire, an off-road capable tire may or may not be approved by the DOT. In the United States, such a tire approved for street use will be marked with a DOT code (U.S.), which identifies the tire as street legal. Tires which are not approved for street use will typically be labeled "Motocross Use Only" or "Not for Highway Use". Street legal, knobby tires are generally not suitable for long distances on roads or paved surfaces because of poor NVH properties and excessive wear on the soft rubber.

All-terrain

Depending on the design, an off-road tire may be designated "all terrain", meaning it is intended for use both on- and off-road. Such tires attempt to compromise between grip on loose terrain and safety or comfort on paved roads. Some tires, such as the bar grip used on United States military vehicles in World War II, accomplish this by separating the tire into distinct on-road and off-road tread zones. Modern all-terrain tires typically employ hybrid tread patterns and tougher compound to increase the wear life under mixed-surface conditions.

See also

• Bicycle tire
• Motorcycle tire
• Paddle tire - For use in sand and mud
• Off-road motorcycles
• Off-road vehicles
• Bar grip
• Cyclo-cross bicycle
• Mountain bike
• Rolligon