The information on the side of the tire: How to read your tires correctly
The regulations and designations for car tires are legally defined in Germany by §36 StVZO. This also stipulates that car tires are standardized in accordance with the European regulation ECE-R 30. Letters, numbers and symbols on the side of the tire represent important information. But what exactly do the respective markings stand for and what other information from the vehicle documents does the holder have to take into account?
Information on tire sizes in the vehicle documents
In your vehicle registration document you will find the necessary information about which tire sizes are approved for your respective car. In lines 1 to 15.1 or 15.2 of the so-called “Registration Certificate Part 15.3”, the prescribed tire dimensions are specified for each axle. If different sizes are planned for the front and rear axles, the data in the two lines will differ.
The sizes entered in the registration certificate do not necessarily have to correspond to the dimensions of the tires currently installed on your vehicle. Further tire sizes approved by the manufacturer can be found in the vehicle documents, which are given to you when you buy the car or can be requested from the brand manufacturer. The so-called CoC document (Certification of Confirmity) lists tire dimensions that differ from the specifications in the vehicle registration document. Only if a broader variant of the tire size defined in the vehicle registration document is listed can it be mounted on the axles of your car.
The most common information on tire sizes can be found on the side of the tire. Among other things, the tire width is listed here, which is generally given in millimeters. The various cross-sectional widths of the tires range from 125 to approx. 335 millimeters. The available tire widths increase every 10 millimeters. The width of your already installed tires may differ slightly from the defined data and is also dependent on the width of the rims used.
A tire with dimensions on the side of the tire, for example 205/55 R16, has a nominal width of 205 millimeters.
The standardization of tires also enables mounting on rims of different sizes. In some vehicles, however, the tires may only be mounted on certain rims. This also applies to the use of snow chains, which are only permitted for certain tire and rim widths. You will find the necessary information in the vehicle documents or in the operating instructions for your car.
The profile cross-section of a tire, which is defined by the ratio of tire height to tire width, is given in percent. In the 205/55 specification, the number 55 means that the tire cross-section corresponds to a height of 55 percent of the tire width (205 mm). A falling ratio of, for example, 205/45 results in a lower tire flank and is particularly popular with sporty or tuned cars.
According to the regulations, only tires of the same type may be mounted on your car. This avoids mixed tires that are only approved in exceptional cases.
The type of tire is identified by letters on the side of the tire. In the 205/55 R 16 specification, the R stands for radial and refers to the type that is typical today with radially running carcass threads inside the tire. Diagonal tires (marked with a D) were previously widespread and can only be fitted to classic cars today.
If the letter R is followed by an F, it is a run-flat or emergency tire. This type of tire has reinforced sidewalls, which should ensure the stability of the tire even after a puncture. Despite tire damage, you can still get to the nearest workshop with this type of tire without having to fit a spare wheel.
The number after the letter that indicates the tire width indicates the rim diameter in inches. A tire with the specification 205/55 R 16 is designed for mounting on rims with a diameter of 16 inches. The usual dimensions are between 10 and 20 inches.
Load index and speed index
The next figure on the side of the tire is the load index. It is abbreviated to LI and is also called the load capacity or load index. This shows the resilience of the tire.
Each LI value is assigned a specific load capacity of the tire at an air pressure of 2,5 bar. In order to be able to determine the load capacity of the tire with the index, there are tables with all available values.
For a tire with the specification 205/55 R 16 91 V, the 91 stands for the load index. For the code number 91, for example, the maximum load-bearing capacity of 615 kg at an air pressure of 2,5 bar is specified. It should be noted here that a lower tire pressure also results in a lower load capacity of the tire.
Speed or speed index
The last letter in the specification of the tire stands for the speed index. This provides information about the maximum speed with which the tires can be driven. The tire with the details 205/55 R 16 91 V, for example, has a permissible top speed of 240 km / h (V). This data can also be viewed in the tables defined for this purpose.
If your tires have a special tread pattern, labels such as rotation, direction of rotation or direction can be found on the side of the tire, together with an arrow that indicates the direction of rotation. The correct running direction must always be observed when mounting the tires.
Winter and all-season tires
When buying winter tires, you should not only pay attention to the quality and proven driving characteristics, but also to the so-called “Alpine” symbol. It consists of a three-pointed mountain pictogram with a snowflake in the middle.
For all winter tires that have been produced since January 1, 2018, this symbol is mandatory on the side of the tire.
The previously valid M + S mark (mud and snow) is no longer sufficient for newly manufactured winter tires. Until September 30, 2024, however, tires that have already been produced with the M + S mark still meet the winter tire requirement, so that consumers do not have to replace winter tires that have already been bought.
It is also possible that winter and all-season tires that are marked with the “Alpine” or M + S symbols have a lower speed index and may therefore not be driven up to the vehicle's own maximum speed. Here, the legislator requires that the driver is informed of the maximum permitted speed via a sticker in his field of vision inside the vehicle.
Wear indicators (TWI) can be found in six places on the side of the tire on both sides of the edge of the tread. At the level of the letters “TWI” (Treadwear Indicator) there are raised areas on the bottom of the main tread grooves, which provide information about the wear and tear of the tire.
In addition to the TWI indicators, you should regularly check the tread depth of your tires and make sure that tires already lose grip on wet and snow below a tread depth of 3-4 millimeters.
Production date, “DOT number” and “E” approval mark
You can also determine when the tire was manufactured on the side of the tire. The four-digit sequence of the DOT number is decisive as an impression. The number pad, which is set off in an oval, is relevant for the date of manufacture. A tire with the number 0816 was manufactured in the eighth week of production in 2016. Please make absolutely sure that a new tire should never be older than two years. Depending on their age, unused tires have poorer technical properties and endanger the safety of your vehicle.