*insert tire conversion chart*
A majority of tire sizes will begin with a letter which will help identify what vehicle or service the tires are made for. Sizes that don’t include a letter in the beginning indicate that the tire is in metric sizing. These sizes are usually used on cars from Europe but can also be placed on vans and sport utility cars. Metric tire sizes and P-metric tire sizes are the same by dimension but carry different weight
P: Tires that have “P” at the beginning of the size are generally used for passenger vehicles and are to be considered “P-metric” size. This would include cars, light duty trucks which carry ¼ or ½ ton of capacity, minivans, and sport utility vehicles
T: Tires that begin with a “T” indicate that it is a temporary tire, this tire is only to be used for a small period of time
LT: Tires that begin with “LT” it means that the tire is a light truck tire which is designed for trucks that carry heavy loads. This would include medium and heavy duty, carrying ¾ and 1 ton capacities including pickup trucks and sport utilities cars. If tires end with “LT” it means the tire is “numeric,” “widebase,” or “flotation” light truck size which are used for vehicles that carry heavy cargo and tow trailers. These vehicles typically use rims that are 16.5 inches in diameter or in other cases even wider sizes. This aids in driving on top of dirt or surfaces that have sand on them. These tires typically carry ½, ¾, and 1 ton capacities.
C: The “C” means that the tire is a commercial tire which means that it belongs on vans or trucks used for delivery which carry large loads. These tires also are branded by the services they are meant to perform.
ST: When beginning with “ST” it means that the tire is a special trailer tire which was designed to be used on boats, and car or utility trailers. These tires should never be used on regular cars, vans, or light trucks
After the letter that indicates what service the tire will do there are numbers, these numbers indicate how wide a tire is from outer sidewall to the inner side wall in millimeters. This number can be converted into inches by dividing the width by 25.4 Tires Profile and Sidewall Following the numbers that indicate section width would be the number that identifies the tires profile or aspect ratio. This number shows the height of the tires sidewall from the start of the rim to the end of the tread pattern in percent form. The bigger the number the taller the tire will be and vice versa. You would multiply this number with the results you got from converting the section width into inches.
The letter “R” in a tire size shows the tires internal construction and will be found after the number that identifies the profile and sidewall. The tire’s body plies radiate outwards from the imaginary center of the wheel and are extremely popular tires to purchase.
Tires with a “ZR” on them are considered to be Z-speed rated tires. The “Z” indicates the tires speed rating and the “R” as previously stated is the internal construction, any other speed ratings will be in the tires service description.
The number after the “R” would be the diameter of the rim that fits into the tire. These diameters are measured in inches and are known are inch rim sizes. These are very commonly used on a majority of all types of vehicles.
At the end of a tire size if there is a number with an S attached to it, that number will identify the load index and the speed rating that the tire offers. These are required on all tires made after the year 1991.