Tyre DOT Code: what is it and how to read it

DOT is the abbreviation for “Department of Transportation” and indicates a unique tyre code which is a series of 7 to 13 letters and numbers printed on the sidewall of a tyre (the vertical surface of rubber above the wheel). DOT is usually followed by a combination of letters and numbers that provide information on the tyre’s place of manufacture, as well as its type and age.

Information on the age of your tyres is contained in the four numbers at the end of the DOT code. This date code is often encircled by a raised rubber oval. If you see the letters DOT, but they are not followed by any other letters or numbers, look on the other sidewall. Manufacturers are only required to stamp the complete tyre identification number on either the inside or outside sidewall, but not both.

The first two numbers of the 4-digit DOT date code (which, again, appears at the very end of the string of letters and numbers that start with DOT) indicate the week that the tyre was manufactured. The last two numbers of the date code tell you the year of manufacture. In the example below, the date code is 0517, which means that the tyre was made in the 5th week of 2017. If the date code has only three digits, it means that your tyre was manufactured before the year 2000, when a different system was used.

Apart from the DOT designation and date code, you will find other letters and numbers on your sidewall containing additional information about your tyres. These include the other letters and number in the tire identification code itself, which are between the DOT marking and the date code. These additional characters come in either two or three blocks.

• The first block tells you the plant where the tyre was manufactured.
• The second block is a tyre size code.
• The third, which is optional, is an internal individual product code defined by the tyre manufacturer.

Elsewhere on the sidewall, the most common markings are for tyre size, speed index and load index. These numbers are usually bigger than the DOT code and generally appear in the following order: nominal section, width, height-to-width aspect ratio, wheel diameter, load index and speed index. The load index is a 2 to 3-digit number that can be used (by referring to load index chart) to look up a tyre’s maximum load when properly inflated. The speed index is a letter that can be cross-referenced to learn the maximum safe speed for a tyre.

A common misconception is that high-mileage tyres are immune to ageing. While some have anti-ozonant chemicals added to counteract the effects of ageing, the weakening effect of the years is inevitable for all tyres.