Off-road tires, often referred to as OTR tires, are designed for wheel loaders, dump trucks, graders, telehandlers and other construction equipment operating on unpaved, abrasive or uneven ground. Compared with highway tires they feature a reinforced carcass, thicker sidewalls and a coarse tread pattern that resists cutting, chunking and puncture damage from rock, debris and compacted soil.
Construction and Design
Two carcass types are in use: bias-ply (diagonal) and radial. Bias-ply construction uses crossed fabric plies and remains common in quarry and mining applications because the stiffer sidewall resists cuts and impacts from sharp rock. Radial construction, with steel belts running circumferentially, offers lower rolling resistance, better heat dissipation and improved flotation on soft ground, and is standard on modern wheel loaders and articulated haulers.
Load capacity is expressed as a ply rating (PR), a nominal index such as 12PR, 16PR, 20PR or 28PR that indicates equivalent load-carrying strength rather than the physical number of fabric layers.
Tread Patterns and Classification
The Tire and Rim Association (TRA) defines tread-pattern service classes used across the industry: L-2 (smooth to shallow-lug rib tread for soft, non-abrasive soil), L-3 (general-purpose traction tread), L-4 (deep, rock-service tread for abrasive quarry ground) and L-5 (extra-deep tread for maximum cut and abrasion resistance). Selection depends on ground conditions, cycle speed and expected tread wear life.
Load Rating and Inflation Pressure
For haul trucks and loaders operating at sustained speed and load, manufacturers specify a TKPH rating (tonne-kilometers per hour), which limits the heat buildup inside the tire and determines the maximum safe combination of load and travel speed. Exceeding the TKPH limit accelerates belt separation and casing failure. Recommended inflation pressure varies by tire size, load and application and is specified individually by the tire or equipment manufacturer rather than as a single universal value.
Central Tire Inflation Systems (CTIS)
Central Tire Inflation Systems allow the operator to adjust tire pressure while the machine is moving, lowering pressure for better flotation and traction on soft or uneven terrain and raising it for reduced rolling resistance on hard surfaces. CTIS is integrated by the equipment manufacturer or added as an aftermarket kit at the wheel and axle level; it is not a feature supplied by tire manufacturers themselves, since the tire itself remains a standard pneumatic product independent of the inflation-control hardware.
Standards and Specifications
Dimensional and load data for off-road tires are published by the Tire and Rim Association (TRA) in the United States and by the European Tyre and Rim Technical Organisation (ETRTO) in Europe, covering size designations, load index tables and corresponding inflation pressures. The ISO 4251 series addresses tyres and rims for earth-moving machinery, defining nomenclature, dimensions and marking requirements used for equipment selection and procurement.