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LT: Designates that this is a light truck tire. Load index and speed rating are sometimes not mandatory for flotation sizes, but must be for any tire approved for street and highway use. 2- or 3-digit number: Load index; see table below. 1- or 2-digit/letter combination: Speed rating; see table below. Additional marks: see subheading below.
The wet grip index (WGI) is calculated from the results of two tests specified in the regulations. The first test measures the maximum achievable average deceleration of a vehicle as it slows from 85 ± 2 km/h (52.8 mph) to 20 ± 2 km/h (12.4 mph). The second test (the "skid trailer" test) is usually performed using a tow vehicle and trailer.
These represent the tire's resistance to the generation of heat at speed. Tires graded A effectively dissipate heat up to a maximum speed that is greater than 115 mph. B rates at a maximum between 100 mph and 115 mph. C rates at a maximum of between 85 mph to 100 mph. Tires that cannot grade up to C or higher cannot be sold in the US. [9]
English: Diagram showing a side view and underside of a conventional 18-wheeler semi-trailer truck with an enclosed cargo space. The underside view shows the arrangement of the 18 tires (wheels). Shown in blue in the underside view are the axles, drive shaft, and differentials. The legend for labeled parts of the truck is as follows: tractor unit
The standard test speed for tire uniformity machines is 60 r/min of a standard load wheel that approximates 5 miles per hour. High speed uniformity machines are used in research and development environments that reach 250 km/h and higher. High speed uniformity machines have also been introduced for production testing.
The European Tyre and Rim Technical Organisation (ETRTO) exists to specify and harmonise sizes of rims and their associated pneumatic tyres across the European Union.ETRTO sizes apply to rims and tyres for vehicles of all types, including bicycles.
The first deliberate uses of bar grip tyres as off-road tyres, were developed pre-war as truck tyres particularly for army use. They used crosswise tread bars for grip, arranged in a helical pattern. [4] A helical pattern was used to avoid the uneven rolling radius and vibration of a tread with simple crosswise bars and large gaps between.
The State truck size and weight regulations apply to the Federal Aid System routes that do not have Federal limits. The weight and size of CMVs are restricted for practical and safety reasons. CMVs are restricted by gross weight (total weight of vehicle and cargo), and by axle weight (i.e., the weight carried by each tire).