How to read a DOT code

Even a tyre whose tread still looks deep may have aged. The way to find out when a tyre was made is the DOT code on its sidewall. Whether you're buying new tyres or looking at a used car, checking this code takes a few seconds and can protect you from a serious risk.

Where is the DOT code?

DOT stands for the US Department of Transportation, but this code is found on tyres sold all over the world. It is a string of letters and numbers on the sidewall starting with the letters "DOT". For example:

DOT 4B2X 7Y9R 2324

The full code may not appear on both sidewalls. The last part, which shows the production date, is sometimes only on one side. If you can't find it, look at the other side of the tyre.

The last four digits: production date

The four digits at the very end of the code are the tyre's production date:

• First two digits: Week of manufacture (01–53)
• Last two digits: Year of manufacture

2324 means week 23 of 2024, which is early June 2024. 0821 means week 8 of 2021, which is February 2021.

On tyres made before 2000, the date was written with three digits (for example 189: week 18 of 1999). A tyre with a three-digit DOT code is at least 25 years old today and must not be used under any circumstances.

What do the other characters mean?

• First two characters (4B): The code of the factory where the tyre was made
• Following characters (2X 7Y9R): Size and manufacturer-specific type codes

The part that matters to the driver is the last four digits.

Why do tyres age?

A tyre is made of rubber, steel, fabric and many chemicals. Over time, oxygen, sunlight (UV), heat and ozone reduce the rubber's flexibility. As a result:

• Fine cracks form on the sidewalls and at the base of the tread.
• The rubber hardens and grip drops, especially on wet surfaces.
• The risk of tread separation rises at high speed and in hot weather.

This process continues even if the tyre is never used. A spare tyre sitting in the garage also ages.

How many years should a tyre be used?

There is no legal age limit, but the general recommendations of tyre and car manufacturers are:

• After 5–6 years, the tyre should be checked by a tyre specialist every year.
• Tyres over 10 years old should be replaced, however deep the tread is.

These periods are shorter depending on conditions of use. Tyres on cars that are always parked in the sun, are run at low pressure for long periods or operate at high temperatures age faster.

When buying new tyres

A "new" tyre may have been sitting in the shop for some time. It is normal for a properly stored tyre to be sold a few months or a year or two after production, and this does not noticeably affect its performance. Even so:

• Make sure the production dates of all four tyres are close to each other.
• Don't let a tyre with a very old production date be sold to you as "new". Check the date before it is fitted.

When buying a used car

On a used car, check the DOT codes of all four tyres and the spare. Even if the tread looks good, tyres older than 7–8 years mean a replacement cost in the near future. You can take this into account when negotiating.

Quick check

1. Find the "DOT" marking on the sidewall.
2. Read the last four digits: the first two are the week, the last two the year.
3. Work out the tyre's age.
4. Check the sidewalls for cracks.
5. If in doubt, show it to a tyre specialist.