The side wall contains information for the user about the size of the tyre. These markings tell us about the intended use of the product, the load capacity and size of the tyre, and its durability at high temperature and speed. The rules for tyre markings are laid down in the ECE-R 30 European standards. The marking on the side wall of a tyre reveals the key parameters of the product. The size of a tyre can always be found printed on its side.
195 is the width of the tyre. The first value in the tyre code is given in millimetres. The marked width of a tyre increases in steps of 10 mm, and so we can encounter models marked 175/65R 14, 185/65 R14 and 205/55 R16. In reality the width of tyres differs slightly from the marked values, particularly with different manufacturers. For example, the number 195 in the product marking means that the width of the tyre is 195 mm. This is the distance between the most extreme point on the outer side wall and the most extreme point on the inner side wall, when the tyre is mounted on a wheel of the appropriate width. This dimension is called the cross-sectional width of the tyre.
60 is the tyre aspect ratio. This next value in the tyre code indicates the profile of the model. It represents the percentage ratio of the height of the profile to the tyre width. This tells us what percentage of the width is accounted for by the profile height. For example, in a tyre with the code 195/60 R15 the aspect ratio is 60, which means 60% of the width of the tyre. 60% of 195 mm is 117 mm. Tyres with lower sides are called low-profile tyres, and normally have ratios of 50, 45 and 40. Higher-profile tyres usually do not have the aspect ratio marked; for example in the case of the 165R13 tyre the aspect ratio is 80.
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 195/60 R15 tells the user that the model has body layers running radially from the centre of the wheel. Radial tyres are the most popular tyres, accounting for 98% of total worldwide sales.
15 is the value that tells us the diameter of the wheel on which the tyre should be mounted. This parameter is expressed in inches.