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What Information Can Be Found On A Tire?

The sidewall of a typical tire is imprinted with myriad codes and numbers that are used to identify the size and physical features of that tire as well as details relating to its manufacture.

Tire Size

Your tire size can be found on the sidewall of your current tire and is a sequence of numbers and letters.

  • The first three digits displays the width of the tire in millimeters. This measure is across the tread from sidewall to sidewall.

  • The fourth and fifth digits of the tire code that immediately follow the tire width is the aspect ratio or profile height of the tire sidewall. It is expressed as a percentage of the tire width.

  • Radial tires are marked with the letter R. Radial tires are constructed with the cord plies positioned at a 90 degree angle to the direction of travel to give the tire additional strength. Almost every new tire manufactured today is a radial tire.

  • The next two digits represent the size of the wheel rim that the tire can be fitted to. It is also the diameter of the tire from bead to bead.

Speed Rating

The speed rating of a tire is represented by a letter of the alphabet at the end of the tire size code and indicates the maximum speed capability of the tire. Tires receive a speed rating based on a series of tests which measure the tire capability to handle a set speed for a prolonged period of time.

Load Index

The load index provides information on the maximum weight capability for the tire. The load index is a numerical code that can be located just after the tire size marking and before the speed rating.

Date of Manufacture

Your tire is also printed with information about when and where the tire was manufactured. This is represented by a series of letters and numbers which starts with the letters DOT (meaning the tire exceeds Department of Transport safety standards).

  • The first 8 characters that follow DOT are essentially a serial number used by the manufacturer to identify the tire and in which production facility it was made.

  • The last four digits, usually presented in a small window can help you to identify the age of the tire.

  • The first two digits represent the week of the year the tire was produced from 1 to 52. The last two digits represent the year. 

Reinforced

Tires with an increased load index are often marked to show that they have been reinforced to handle extra weight. Common markings to show this are: RF, REINF and RFD.

Run Flat

Run flat tires are specially designed with strengthened side walls so that, in the event of a loss of pressure such as a puncture, the tire can hold the weight of the vehicle and continue to be used for a short time until you can reach an appropriate place to stop and have the tire replaced. Possible symbols for this are: ROF, EMT, RFT, ZP, SSR and DSST.

Homologation

Some tires are intended specifically for use with certain vehicle makes for added performance benefits. These tires are designed in close co-ordination with the vehicle manufacturer and feature a designated symbol on the sidewall which shows that the tire meets the manufacturer’s exacting standards and has been given OE status. Tires designed for Ford vehicles will have an FO symbol.