A lot of people can get virtually lost in the world of technical details concerning their vehicles, so tire size explanation can help those who are absolutely unfamiliar with tire size specifications. In fact, information contained in those long numbers placed on tires needs to be correctly decoded. Each figure is aimed to help you in choosing the right tire for your auto.
Variety of tires and tire codes
Each tire has individual alphanumeric tire code located on the tire sidewall. In some cases both inner and outer sidewalls have figures on their surfaces. These figures encrypt tire dimensions and major limitations (for example, how much load it can bear or what highest speed it can stand). In comparison with old models new tires have the Uniform Tire Quality Grade ratings (namely, information about tread wear, temperature resistance, traction, etc.).
There are 3 major sizing systems, which can be found on vehicles:
- ISO Metric sizing system (the most common);
- Light Truck Numeric System (found predominantly on trucks, trailers and SUVs and characterized by absence of a front letter);
- Light Truck High Flotation system (is rarely used).
Tire size comprehensible explanation
- Usually combination of figures is preceded by a letter. Letter “P” stands for passenger cars, “LT” – for light trucks (if “LT” follows the numbers, it indicates that this tire is suitable for heavy loads or other vehicles pulling), “ST” – for special trailers for carrying cars or boats, and “T” – for temporary vehicles. You can see that each type of vehicle has its own type of tires.
- The following three numbers indicate cross-section width of the tire. It is the number of millimeters, which you can get if you measure the space between the widest parts of outer and inner sidewalls. This measurement can be done only when the tire is placed on the appropriate wheel.
- The following two numbers after a slash mark stand for the ratio of the tire’s height to width given in per cent. To obtain this figure it is necessary to measure the height of the given tire from rim to tread. Sometimes this figure may be omitted, which means that high-to-width is standard and constitutes 82%.
- After the figures goes another letter, which indicates tire construction. Letter “B” is used to show that this tire is supplied with reinforced belts under the treads (can be rarely found), “D” stands for diagonal fabric carcass (this type of tires is typically used as spares or for light-duty trucks), “R” – for radial fabric carcass (the most common type), “F” – for run-flat. If the letter is omitted, this is a cross ply type.
- The next two-digit number describes the diameter of wheels, for which this tire is suitable. It is given in inches and may range from 8 to 28. Sometimes you can come across half-inch measurements, which signal that the given tire is appropriate for heavy-duty trucks, commercial vans, trailers, etc.
- The following combination of two numbers and one letter reflects load-bearing potential of the given tire and speed rating.
- Additional marks, which may be placed on tires: Mud & Snow, Black/White sidewall, Outlined (Raised) White Lettering, Vertical/Black Serrated Letters, Department of Transportation Code, Side Facing Inwards/Outwards, country of production, etc.
All technical standards are established by the Tire and Rim Association of America.
Now you are more or less familiar with different sizes of tires thanks to our step-by-step guide to tire size explanation. You can effortlessly pick up tires, which are appropriate for your automobile.