How can I discern the size of my tyres? Which tyre indices do I have to pay attention to when buying? Classic questions, that many drivers ask themselves when buying new tyres.
Here you can find an overview of all important tyre markings:
Tyres are usually labelled with certain information. This tyre labelling is standardized and among other things it indicates the speed index, brand, tyre size and the date of production (DOT number). However, only a very few data can be read directly, others are "coded" in various ways. Mytyres.co.uk explains how to read the most important information from the tyre marking.
Behind a number-letter combination such as 175/60 R15 information about the size of a tyre is hidden. The first number refers to the tyre width in millimeters followed by the tyre tread as a percentage relation to the width - for calculating the height of the tyre. In this sample, 60 percent of 175 mm are 105 mm. The letter R indicates a radial tyre and at the end you'll find the wheel diameter in inches. It corresponds to the rim size that is suitable for this tyre.
The information about the tyre size are usually complemented by other values, such as by 91V. The tyre load index specifies the load-bearing capacity of these tyre. The tyre load rating can only be deciphered by using a table - 91 is 615 kg. The speed index is encrypted as well, but by letters. A "V" indicates a maximum speed of 240 km/h (150 mph). 300 km/h (186 mph) are allowed when a tyre is characterized by a tyre speed rating of "Y".
The tyre labelling includes other information such as the DOT number in the form of a four-digit code. It is the tyre's date of manufacturing. The first two digits indicate the calendar week, closely followed by two digits for the calendar year. A tyre with the DOT number 2412 was thus produced in the 24th week of 2012. There is more information to find on special tyres such M + S for mud and snow, CP at caravan tyres, XL for reinforced tyres and R or RF retreaded tyres.
| Speed Index Abbrevation |
Max. Speed Index |
| G | 90 km/h |
| J | 100 km/h |
| K | 110 km/h |
| L | 120 km/h |
| M | 130 km/h |
| N | 140 km/h |
| P | 150 km/h |
| Q | 160 km/h |
| R | 170 km/h |
| S | 180 km/h |
| T | 190 km/h |
| H | 210 km/h |
| V | 240 km/h |
| W | 270 km/h |
| Y | 300 km/h |
| VR | > 210 km/h |
| ZR | > 240 km/h |
When buying tyres you should pay attention to the DOT number - tyres that are more than five years old are not recommended. In addition to the tread depth the tyre age has effects on the performance of a tyre as well. Even if was not in use, but stored properly, physical and chemical processes let the tyres age. After no more than five years it is no longer a new tyre. But how can the tyre's age be recognized? The tyre manufacturing date can be found on the side wall - in the form of the so-called DOT number. DOT stands for US "Department of Transportation".
The DOT number has four digits. The first two digits indicate the calendar week in which the tyre was produced, for example 32. The year of production comes next. So 3214 indicates a tyre from the 32th week of 2014. Will these tyres be stored dry and dark, it is rated as brand-new even in 2016.
Unlike bicycle tyres car tyres have a tube. They rather consist of different layers as the tyre cross-sectionshows. The outermost layer is the tread of the tyre. Usually it is profiled and should ensure that the tyre brings its best performance on the road. Modern tread compounds have a high silica content and provide plenty of grip. Not only they have to adapt well to the prevailing temperature, but also to the road conditions.
The substructure is called carcass. It is usually multilayer and constructed differently according to the type of the tyre. In cross-ply tyres the carcass plies are crossed diagonally, while in radial tyres the cords are arranged at right angles to the direction. These tyres are also called belted tyres. The carcass is protected from damage by the tread and the sidewall of the tyre. Another important component of the tyre structure is the bead. It connects the tyre to the rim by steel wires. Inside the tyre there is a rubber layer for isolation. It prevents the air from escaping.
Tyre Width Rim Width |
Cross section with tyre width and tyre height |
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When it comes to the correct tyre width and the corresponding rim size many motorists are overwhelmed. This is certainly due to the confusing size declarations. While tyre dimensions are given as 195/65 R15 91H for example, at car rims it looks like this: 7J x 17 H2 ET38, 5x112 LK. It is nearly impossible to know whether these two parts fit together. But basically it is not that hard if you know the meaning of the numbers and letters. Tyre SizeA 195/65 R15 91H tyre has a tyre width of 195 mm, which is indicated by the first digit. In addition, its diameter is 15 inches - this is also the size of the rim on which the tyre will be mounted. Thereby the two values are known that are important for the correct rim size. |
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The rim labelling indicates the width in the first place as well. In 7J x 17 H2 ET38, 5x112 LK it is 7 inches. Now you have to know that a rim of this width fits on a tyre with a width of 195 to 225 mm. 205 up to 215 mm are ideal. Behind the "Y" for the rim flange's type and the "x" for well-base rim the rim diameter of 17 inches is given. This rim is therefore not suitable for a 195/65 R15 91H tyre.
In addition to the technical requirements, there are the specifications of the vehicle manufacturer. In the papers you will find the allows tyre and rim sizes. On demand, there is also the COC document with other sizes available.
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