The tyre code on the side of a tyre tells the owner about the intended use of the product, its size, load capacity and durability at high temperatures and speeds. Tyre markings are regulated in Europe by the rules laid down in the ECE-R 30 standards. These relate mainly to the information placed on the side of tyres. These provide us with the most important data about the parameters of a tyre. The tyre code can be found on the side of a tyre.
195 is the tyre width. The first value in the tyre code is given in millimetres. Depending on the particular dimensions, the width increases in steps of 10 millimetres (for example, 175/65 R14, 185/65 R14, 205/55 R16). In fact the width of tyres differs somewhat from what is indicated on the side, and the width also differs from the technical data to a slightly different degree for each manufacturer. The value 195 tells us that the distance from the most extreme point on the outer side wall to the extreme point on the inner side wall is 195 mm. This distance is called the cross-sectional width of the tyre.
65 is the tyre aspect ratio. This second figure in the tyre code tells us more about the profile of the tyre. The figure is the percentage ratio of the profile height to the width. For example, the tyre marked 195/65 R15 has an aspect ratio of 65, and so the height of the side of the tyre is 65% of its width, 195 mm. In this case the profile height is therefore 126.75 mm. When the tyre is lower, the second figure in the code is also smaller – values of 50, 45 and 40 are usual for low-profile tyres. Higher-profile tyres often do not have the aspect ratio included in the tyre code marked on the side.
The letter R means that the tyre has a radial construction. These tyres contain layers of fibres running in a radial direction, at an angle of 90 degrees. The R in the designation 195/65 R15 indicates that the tyre has a radial construction, with body layers running radially from the centre of the wheel. Radial tyres are the most popular tyres, accounting for 98% of the total number sold.
15 is the diameter of the wheel on which the manufacturer recommends that the tyre be mounted, expressed in inches.