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P-metric sizes were introduced in the United States in the late 70s and are installed on vehicles primarily used to carry passengers, including cars, estate cars, sport utility vehicles and even light-duty pick-up vans.
Their load capacity is based on an engineering formula which takes into account their physical size (the volume of space for air inside the tyre) and the amount of air pressure (how tightly the air molecules are compressed).
(R) Construction The “R” stands for radial construction, which is the industry standard for passenger car and light truck tires.
A “B”, “X”, or “-“ in place of the “R” would indicate that the tire has bias ply construction.
A letter from A to Z symbolizes a tyre's certified speed rating, ranging from 5km/h (3 mph) to above 300 km/h (186 mph).
P-metric sized tyres are those with the "P" at the beginning of the tyre size (such as P215/65R16).
However, since Euro-metric sizes have been added over time based on the load and dimensional requirements of new vehicles, tyre manufacturers have designed many new tyre sizes and load capacities around the needs of new vehicles.(65) Aspect Ratio This number is the tire's aspect ratio, or its section height compared to its section width.