Tyre markings explained | Continental tyres

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Tyre markings

Tyre markings

How to read your tyre´s sidewall

 

There is a range of useful information that can be found on the sidewall of a tyre. At first glance, the tyre label may overwhelm the vehicle owner. The tyre designation provides all the necessary information that is of interest to you. It includes the name of the tyre model, but also a sequence of numbers and letters detailing load index, speed rating, the tyre size, the construction and much more. We explain why tyre markings exist, how to read them correctly and what they say about your tyre.

Where can you find all the important information about car tyres?

Even if not all potential tyre designations are listed on the tyres, you will find all relevant dimensions and criteria on the sidewall of the tyre to determine whether a tyre is suitable for a vehicle. If, however, you are looking for all tyre dimensions that are suitable for a vehicle, take a look at the "CoC" (Certification of Conformity). Why is it important to understand the markings? Because car tyres can be distinguished according to various characteristics and criteria, and the labelling also indicates whether the tyre is suitable for a particular vehicle or not. But what does the information on the sidewall of car tyres actually mean?

Size, width and diameter of tyres

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To find out which tyre size is suitable for your car, look at the tyre designation on the sidewall of the tyre. Further possible tyre sizes are listed in the CoC ("Certification of Conformity") document under the points "32. Wheel tyres:" and/or "50. Comments:" (images 1b, 1c).

For example, the tyre might be marked with the designation 205/55R16. This marking represents a nominal width of the tyre of 205 mm, a nominal aspect ratio of 55% (ratio of section height to nominal width). The aspect ratio is given as a percentage. It is the ratio of the height of the sidewall to the tyre width. It is calculated by dividing the height of the tyre section by the width of the tyre section. If a tyre has an aspect ratio of 55, this means that the height of the tyre is 55 percent of its width.

The rim diameter is determined diagonally from rim edge to rim edge, the measurement is usually given in inches – in this case it is 16 inches.

The tyre designation R, which comes before the rim diameter marking, means that this tyre is a radial tyre. Other examples are “B” for Bias-ply or “D” for Diagonal construction.

Radial tyres are the most common tyres on the road today. They’re called radial because the tyre’s internal ply cords are orientated in a radial direction, from one bead over to the other, at right angles to the direction of the tyre’s rotation. Diagonal tyres have replaced solid rubber tyres and are harder overall due to the diagonal fabric layers. The higher resistance means that cross-ply tyres heat up quicker and therefore wear out faster.

Radial tyres are normally used on our roads these days. The radial tyre owes its name to its construction. The cords in the carcass are placed at right angles to the direction of travel and consist of several fabric layers of nylon and steel, which absorb vibrations and unevenness particularly well. It is prohibited by law to use radial and cross-ply tyres at the same time.
 

Passenger tyres have load indices spanning from 75 to 105, where each numeric value corresponds to a specific load capacity. The carrying capacity for each value is described in a load index chart in your vehicle or tyre documentation. The load index (also load capacity index) indicates the maximum load a tyre may be subjected to. However, the load capacity of a tyre also depends on the inflation pressure and the driving speed.

The maximum load must not be exceeded under any circumstances, as this can easily damage the tyre. It is vital that the correct load index is chosen for your vehicle or else safety and tyre life span could be compromised. The load capacity can be found both on the tyre and in your vehicle’s registration certificate. 

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The maximum permissible speed at which you may drive your car is also indicated by a letter. This is the speed index, which can be read in a table that specifies the maximum speeds of all tyres (known as the speed index table). If the tyre operation index is 91V, the speed index V indicates a maximum speed of 240 km/h according to the table.

The maximum speed is indexed alphabetically. A indicates the lowest and Y the highest speed class.

In addition to top speed, the letter also provides information about driving comfort, traction, wear and corner stability. Higher index tyres generally offer better grip and braking performance, but may wear out faster and offer lower performance in cold conditions. As a result, V-, Z-, W- and Y- indexed tyres are generally more suitable for sports and high-performance vehicles that operate in warmer climates.

To obtain better tyre performance, you can fit your vehicle with tyres that have a higher speed index. But when you choose a lower index, you automatically reduce the maximum permitted speed of your car to the value specified for that index.


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The DOT number provides information about the manufacturer's plant, tyre size, brand and tyre age. The first two digits of the DOT number indicate the manufacturer's plant (also called plant code). The next digits represent the size code – the size of the tyre. The following digits are optional and depend on the manufacturer and represent a manufacturer-specific code with which the trademark can be read off. The age of the tyre can also be found on the sidewall; it appears at the end of the DOT ("Department of Transportation") number. The last four digits indicate the production date of the tyre to the week. The first two of these digits indicate the production week (the range therefore spans from "01" to "53"). The last two digits stand for the year of production (e.g.: a tyre marked "DOT XXXXXXX2714" was manufactured in the 27th week of 2014).

The age of the tyres is a decisive safety factor. This is why tyres should be replaced after ten years at the latest – regardless of whether they are summer or winter tyres. But damage to the tyres may also occur earlier, for example due to incorrect storage. For this reason, a workshop should regularly check six-year-old tyres for ageing cracks and damage.

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Example: Decode tyre markings

You have now read a lot about tyre markings. Our goal is to ensure that you can read the markings on the tyre sidewall at any given time. We will summarise what the numbers and letters are standing for and show you how to decode the designations of your tyres perfectly using an example tyre.

Let’s start with the following sequence of tyre markings as an example: 225/45 R 18 95 H

Tyre markings on a car tyre from Continental.



Tyre width

The first number to appear in the sequence is “225”. This number is the nominal width of the tyre (in millimetres) from one sidewall to the other.

Aspect ratio

Following the slash, the next number in the sequence is “45”. This number is the tyre’s aspect ratio – essentially the height of the tyre’s profile outward from the rim represented as a percentage of the tyre’s width. We calculate this number by dividing the tyre’s section height by the tyre’s section width. So, if a tyre has an aspect ratio of 45, that means the tyre’s height is 45% of its width.

Construction

Next in our series of tyre markings is a letter instead of a number. This letter indicates the type of construction used within the casing of the tyre, which in our example is “R” for Radial construction. Other examples are “B” for Bias-ply or “D” for Diagonal construction.


Radial tyres are the most common tyres on the road today. They’re called radial because the tyre’s internal ply cords are orientated in a radial direction, from one bead over to the other, at right angles to the direction of the tyre’s rotation.

Rim diameter

The number “18” in our example represents the diameter of the wheel rim in inches.

Load index

The number after the rim diameter represents the load index. In our example, “95” is a code for the maximum load a tyre can support when fully inflated. Passenger tyres have load indices spanning from 75 to 105, where each numeric value corresponds to a specific load capacity. The carrying capacity for each value is described in a load index chart in your vehicle or tyre documentation. More information on the load index.

Speed rating

Last in our sequence, we come to the speed rating. Letters ranging from A to Z represent the speed rating. Each letter denotes the maximum speed a tyre can sustain under its recommended load capacity. In our example, “H” is equivalent to a maximum speed of 130 mph (209 kph). Even though a tyre is capable of performing at this speed, drivers should not exceed legal speed limits. Read our guide to speed ratings.

Additional markings

After this sequence of information, other letters and symbols may also be present on the sidewall.


In our example, they denote the following:

   

7. Run-flat tyre: We are dealing with a run-flat tyre. This self-supporting run-flat (SSR) tyre can continue to be used in the event of pressure loss thanks to its reinforced walls.

   

8. Original Equipment key: The tyre is a Mercedes Original Equipment tyre with run-flat properties (MOE)

   

9. M+S describes that the tyre is suitable for mud and snow conditions.


10. DOT code: Compliant with Department for Transport vehicle safety standards of the US Department of Transportation (DOT

 11. Week of manufacture: 36th 

12. Year of manufacture: 2016


Find your tyre.

Other markings on the tyre

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As you can see from our overview, there are also other important markings on tyres.

You can also identify the directional tread designation, which marks tyres with special tread with an arrow together with the terms "rotation", "direction of rotation" or "direction" and indicates the direction in which the tyre must be mounted. The rotational direction of tyres is particularly important because if a tyre is fitted from the wrong side, the tread pattern will not be able to drain water properly in bad weather conditions. In addition, some tyres have the inscription "Outside" to clearly indicate which side must be mounted outwards if the tyre has different treads.

Most tyres are labelled "tubeless" or "TL" to indicate that the tyre has no inner tube. In general, passenger car tyres are tubeless, with a few exceptions. “Run flat” tyres are a special form of tubeless tyres. They have emergency operation properties and can still be driven in the event of damage. A run flat tyre can be driven for up to 80 kilometres at a speed of 80 km/h, allowing you to make your way to the nearest workshop. Manufacturers use different codes to mark their run flat tyres. The code "CSR" (ContiSupportRing) can still be found on older Continental tyres, but this has been replaced by the new technology for self-supporting run flat tyres with the code "SSR" (Self Supporting Runflat).

M+S stands for mud and snow and indicates that the tyre is suitable for winter weather conditions with snowy or muddy roads. The M+S symbol, however, is not exclusive to the sidewalls of winter tyres, but can also be found on all-season tyres. In the past, all-season tyres with the M+S symbol were sufficient to meet the winter tyre requirement. According to a new regulation, all winter tyres manufactured from 1 January 2018 must also bear an "Alpine" symbol, a three-pronged mountain pictogram with a snowflake. There is no need to replace tyres with M+S prematurely, a transitional period applies until 30 September 2024. After this period, all winter tyres must bear the new alpine pictogram.

Tyres have a wear indicator which is labelled with the letters "TWI" (Tread Wear Indicator). The TWI is stamped in several places on the tyre, making it easy to see the tread wear from the main tread grooves at the same height. This way, you always know when too much tread has worn off and the tyre may no longer be driven according to the rules – less than 1.6 mm.

Vehicle manufacturers are focused on customising and optimising their vehicles and developing what are known as OE tyres in cooperation with Continental. A special symbol is used to identify OE tyres. "OE" stands for original equipment and indicates that the tyres meet the manufacturer's specifications and are recommended for a specific model. The development process runs parallel to the development of the vehicle. The tyres are factory-fitted and are ideally matched to the corresponding model and chassis.