European tyre markings are subject to the ECE-R 30 standards. These standards define in particular the markings on the sidewalls of tyres, as they contain the most important information for drivers. These include the tyre size.
215 - tyre width. The tyre width is given in millimetres and can be found on the sidewall of a tyre as the first value. Subsequent tyre sizes vary by 10 millimetres, e.g. 175/65 R14, 185/65 R14. The actual tyre width is often slightly different from the stated width, the differences largely depend on the manufacturer. The designation 215 is the cross section width of the tyre, measured on a tyre installed on a rim, between the extreme point of the inner sidewall and the extreme point of the outer one.
55 - aspect ratio. The aspect ratio is the value indicated in second place in tyre size designations. It defines the percentage ratio of profile height to tyre width, e.g. for the 215/55 R16 model, the height of the tyre profile is 55% of the width of 215 mm. In this example, the actual aspect ratio is 118.25 millimetres. Low profile tyres are those with type designations: 45, 40, 50. High profile tyres often do not include a profile height.
R - means a tyre of radial construction. Models of this construction account for more than 98% of total sales, so they are the most popular. The body of a radial tyre is made up of fibres arranged in layers and running radially. These fibres are arranged laterally at an angle of 90 degrees to the tyre. On the 215/55 R16 model, the carcass is radially distributed from the centre of the wheel.
16 - it is a value indicating the diameter of the rim on which the tyre is to be installed. It is expressed in inches.