The side of a tyre contains a tyre code, which gives information concerning the tyre’s intended use, size, load capacity and durability during travel at high speed or high temperature.
These markingss are very important for drivers, because they tell them about the most important parameters of the tyre – for this reason they are regulated in the European ECE-R 30 standards.
The tyre code can be found on the side of each tyre.
The first number given on the code on the side of a tyre is its width, such as 195. This value is given in millimetres, and denotes the distance between the extreme outer and inner points when the tyre is mounted on a wheel appropriate for its size. The width affects the tyre code – a difference of 10 millimetres between two tyres means that they have different codes. The actual width of tyres often differs by several millimetres from the number given on its side – this variability depends on the particular manufacturer.
In second place in the tyre code is the aspect ratio. This is the ratio of the profile height to the width of the tyre, for example, in the code 195/70 R15, the number 70 means 70% of the tyre’s width of 195 mm. Low-profile tyres are marked with numbers like 45, 50 and 40, while higher-profile tyres often have no ratio marked; for example, the 165R13 actually has an aspect ratio of 80.
Radial tyres account for 98% of total sales, and are marked on the side with the letter R. These tyres contain layers of fibres running in a radial direction, at a right angle across the tyre. In a tyre marked 195/70 R15, the body layers run radially from the centre of the wheel.
15, the last number in the tyre code, tells users about the recommended diameter of the wheel on which the tyre should be mounted. This is expressed in inches.