Tires age even when they are not driven
A tire does not only lose quality through wear. Rubber contains plasticisers and protective agents that evaporate over time. Oxygen, ozone, UV light and temperature changes make the compound harden. A hard tire grips less well, especially on wet and cold roads. That is why it pays to know a tire's age, even if the tread still looks deep enough.
How to read the DOT code
On the sidewall you will find a string of characters starting with DOT. DOT stands for the US Department of Transportation, whose marking has become the worldwide standard. The string contains a plant code, often size and construction codes, and at the end four digits, usually in an oval. These four digits are all you need:
- The first two digits are the calendar week of production.
- The last two digits are the year.
Example: <strong>2219</strong> means calendar week 22 of 2019, i.e. late May 2019. The full DOT code is often only on one side of the tire. If you can only find part of it on the outside, look on the inner side.
If there are only three digits at the end, the tire was made before 2000. At that time only one digit was used for the year; tires from the 1990s are also marked with a small triangle. Such tires no longer belong on the road.
In the tire size calculator you enter the four digits and immediately see the production week, year and exact age in years and months.
How old can tires be?
In Germany there is no legal maximum age for car tires. The only requirement is a minimum tread depth of 1.6 mm (§ 36 StVZO). Experts, tire manufacturers and motoring clubs agree on the following recommendations, though:
| Age | Recommendation |
|---|---|
| up to 3 years | As good as new in terms of age |
| 3 to 6 years | Uncritical, check tread and condition |
| 6 to 10 years | Have them checked at least once a year |
| over 10 years | Replacement strongly recommended, even with good tread |
These limits are guidelines. A tire that stood in the sun for years or was often driven underinflated may need replacing earlier. A tire stored cool and dark lasts longer.
There is a fixed age limit for trailers approved for 100 km/h in Germany, however: their tires must be less than six years old. For caravans and horse trailers it is worth checking the DOT code before every season.
Signs of aged tires
- Fine cracks in the sidewall or between the tread blocks
- A hard, shiny surface that barely gives under a fingernail
- Bulges or deformations on the sidewall
- Noticeably poorer grip in wet and cold conditions
Bulges are a warning sign of damage to the carcass. Such a tire must be replaced immediately.
What to check when buying tires
New tires are not always freshly made. They may spend some time in storage before being sold. If stored properly, that does little harm. In the trade, tires up to about three years after production are usually regarded as new. If you want a recent date, ask for the DOT code before buying. With used tires the age matters even more: a set with good tread but eight years behind it is rarely a bargain.
Storing tires properly
If you switch between summer and winter tires, you can slow down ageing. Store the wheels somewhere cool, dry and dark, away from heaters, electric motors and solvents. Tires on rims are best hung up or stacked lying flat. Tires without rims should stand upright and be turned a little every few weeks.
Conclusion
The four digits at the end of the DOT code reveal the age of every tire. From six years, have them checked regularly; replace them after ten years at the latest. Which size a new tire may have is explained in the main guide Tire size explained. And before winter, take a look at the winter tire rules.