The size on the sidewall of a tyre is intended to inform the owner of its basic characteristics.
195 - tyre width. The key value in tyre size is at the front and is expressed in millimetres. The width shown on the sidewall of a tyre changes every 10 millimetres, which is why we are dealing with models such as 175/65 R14, 205/55 R16 or 195/50 R15. In fact, the width of tyres is slightly different from the official parameters, although it depends mainly on production methods. A value of 195 informs the user that the width is 195 mm. This is the distance between the extreme point of the outer sidewall and the furthest point of the inner sidewall as measured when the tyre is well positioned on the rim. The dimension described is called the cross section width of a tyre.
50 - aspect ratio. The second value in the tyre size is an indicator of the profile of the model. In practice, this is a percentage of the sidewall height in relation to the width of the tyre. Using the example, with a tyre size of 195/50 R15, a profile of 50 should be noted, so the profile height is nothing more than 50% of the model width, i.e. 50% of 195 mm. More specifically, the user can thus learn that the tyre profile is 97.5 mm high. Lower values in the tyre size, i.e. 50, 45 or 40 for the aspect ratio, are characteristic of low profile tyres. High profile models often do not include the aspect ratio in their size, which is why some models have an inscription, e.g. 165R13 for a tyre that has a profile of 80.
R - radial structure of a tyre. A radial tyre contains layers of fibres that run radially from the centre of the wheel at an angle of 90 degrees. In other words, the presence of the letter R in a tyre size such as 195/50 R15 means that the product is based on a radial structure with carcass layers running radially across the tyre. Radial tyres account for 98% of the market for tyres sold, which is a proof of their extraordinary popularity.
15 - the value by which we learn about the diameter of the rim indicated for a given tyre model. This information is expressed in inches.