The side of a tyre is full of numbers and letters, but what do the different symbols actually mean?
Legal regulations
Tyres are standardized in the Europe according to the regulation ECE-R 30, as the road traffic licensing regulations (StVZO, § 36) are highly detailed and monitored. The legislature also states what information must be provided on the sidewall of the tyre. The manufacturer's name - usually printed large - and the tyre type are listed there. But there is more information to be found. Our example: We have a tyre with the number combination 195/60 R 15 88 V - this is always the same structure, and only the numbers and letters may vary.
The dimensions of the tyre
195/60 R 15 88 V . In our example, the first two digits, separated by the slash, indicate the tyre size. The tyre is thus 195 millimetres wide, the ratio of its height to the width is 60 percent. The lower the percentage, the lower the edge of tyre.
Radial-ply tyres
195/60 R 15 88 V . The R in 195/60 R 15 88 V indicates the design, namely a radial tyre. Sometimes the word "Radial" is printed also on the flank. Since the 1980s, radial tyres have been used on passenger cars almost exclusively, so that the name has become obsolete. Nevertheless, it is still printed there. Diagonal tyres, as they used to be, are nowadays only mounted on agricultural machines, vintage cars and sometimes also motorcycles. The indicator for tyres of diagonal kind would be a letter D.
Rim diameter
195/60 R 15 88 V . The third digit of our example combination 195/60 R 15 88 V normally indicates the rim diameter in the unit of measure, most commonly an inch. However, some manufacturers also use millimetres, but the difference is easily noticeable because of the magnitude. The size in inches usually ranges from 10 to 20, whereas that of millimetres is between 315 and 440.
Load capacity
195/60 R 15 88 . Of course you can also read how much the tyre can carry. The load index, also known as load index or Load Index LI, is in fifth place. The conversion follows a well-found table on the Internet, 88 means in this context a carrying capacity of 560 kilograms at a given air pressure, usually 2.5 bar. The LI specified in the vehicle documents must not be lower than the actual pressure meaning that if specified as 88, tyres must always be installed with a minimum LI of 88. On tyres with particularly high load-bearing capacity there is still the abbreviation RF (reinforced) or XL (extra load).
Speed
195/60 R 15 88 V . The maximum permissible speed at which the tyre may be driven is indicated by a letter at the end of the number plate combination. The speed index V corresponds to 240 km/h. Usually markings range from M for 130 to Y for 300 km/h. The corresponding table for reading is available on the Internet.
DOT marking
In addition to the markings previously described, each tyre also has an encrypted code from the manufacturer, usually a 12-digit number and letter sequence. The last four digits are usually boxed and form the DOT label (Department of Transportation - the label of the American transport authority has become an international standard). Looking at the marking you can read the date of manufacture, listed as a week and year. If the tyres are made before the year 2000, the DOT number consists of three digits only.
Other license plates
If the tyre has a directional binding, it is indicated with the indication "Rotation", "Direction" or "Direction of rotation" and an arrow pointing in the corresponding direction. The inscription "Tubeless" announces that the tyre is tubeless, and it applies to most of tyres are built that way. The wear indicator "TWI" (Tread Wear Indicator) indicates points in the profile where the degree of tread depth can be easily read off. There, the profile is not enough to the depth. If the point is on the surface, the tyre has run to the legally prescribed 1.6 millimetres and must be replaced. 1.6 millimetres, however, is considered to be very borderline, and we advise a tyre from a residual tread depth of 3 millimetres. "M + S" means “Mud and Snow”. For winter tyres, it is not a s reliable indicator, and only an additional snowflake symbol ensures safety. An “E” or “E” in combination with a number indicates the country of the European ECE standard test. Run-flat tyres, namely tyres that are not completely flattened even after damage, carry the symbol ROF or SST, and they have specially reinforced sidewalls. A small ”1” points to particularly quiet tyres, which are certified with a certificate for reduced noise emission.