What does 205/55 R 16 91 V actually mean? - Brief explanation of information on the tyre sidewall

HANOVER – September 12, 2008: A tyre sidewall contains several alphanumerical codes. Some of them help the manufacturer or tyre dealer to identify the products, others give information on the tyre’s size, type, maximum permissible speed and load rating. Recently information of original equipment relevance and on run-flat properties and low rolling resistance has been added.

The European market leader, Continental, has compiled the most important details.

Size and type
Although the label “205/55 R16 91V" doesn’t say much to the tyre layman, it is really rather simple. “205" specifies the tyre’s nominal width in millimetres. The number “55" refers to the nominal aspect ratio, i.e. the ratio of the tyre’s height to its width. In this case, the height of the sidewall is 55 percent of the nominal width.

The abbreviation “R" says something about the construction and describes the way the cords of the casing are arranged. A distinction has to be made here between two abbreviations: “R" stands for “Radial". In radial tyres, the separate cords of the casing lie transverse to the direction of travel. The advantage is higher speed resistance, better grip and more comfortable driving properties than with diagonal tyres, which were previously the norm. For these reasons diagonal passenger tyres have not been mass-produced in Europe for more than 30 years now. They are still available, however, for utility vehicles and as special tyres for extreme off-road use. Their casing cords run over the tyres diagonal to the direction of travel, they have exceptionally high working loads and are more robust than their younger counterparts.

The number “16” in the size data refers to the rim diameter in inches (1 inch = 2.54 cm).

Load index and speed symbol
“91” is the tyre’s load index (LI). There is a standard conversion table for converting this numerical code to the maximum tyre load. It starts at 50 (= 190 Kg) and progresses in increments of one up to 124 (= 1,600 kg). In the present example, this means that a tyre can be loaded with a maximum of 615 kilograms. The speed symbol (GSY) “V” – indicating the maximum permissible speed – is indicated right after load rating “91”. In this case, the tyre is V-rated, i.e. approved for speeds of up to 240 km/h. Other common speed symbols are T (up to 190 km/h), H (up to 210 km/h), W (up to 270 km/h) and Y (up to 300 km/h). The maximum speed of true ZR (radial construction) tyres is not standardised. Confirmation from the tyre manufacturer is therefore required for speeds in excess of 240 km/h. Together a tyre’s load index and speed index constitute the passenger tyre’s service description.

Winter tyres – only really safe with the “snowflake on the mountain” symbol
Road user safety is the number one priority of Continental’s tyre developers. That is why Continental offers both summer and winter tyres. Each tyre type optimally ensures high safety requirements only in the appropriate season. A genuine winter tyre is easy to identify from the numerous sipes on the tyre and the two typical symbols: “M+S" (“Mud and Snow“) and the “snowflake on the mountain" symbol, a clear indication that it really is a winter tyre.

Tyres that bear this symbol have been tested against a reference tyre to demonstrate their winter suitability. Continental therefore strongly advises customers to keep an eye out for this additional label when buying winter tyres.

Safe tread depth
The abbreviation “TWI“ stands for tread wear indicator. Crossbars are evenly distributed in the main longitudinal profile grooves over the tyre circumference. When the legally defined minimum tread depth of 1.6 millimetres is reached, the crossbars are flush with the tread blocks. Numerous tests conducted by leading car magazines and tests performed by Continental itself prove that the safety reserves of summer tyres under wet conditions significantly decrease with a residual tread depth of less than three millimetres.

A raindrop on the sidewall of new Continental summer tyres indicates the minimum tread depth recommended by Continental for driving under wet conditions. In the case of winter tyres, already a tread depth of four millimetres provides only minimal safety reserves on typical wintry roads. With less tread depth, sipes no longer have sufficient traction on snow or ice. The winter TWI is indicated by a snowflake symbol at a residual tread depth of four millimetres. Winter tyres with a residual tread of less than four millimetres are no longer approved as winter tyres in Austria.

“TL” stands for tubeless tyres
A closer look at the tyre also reveals a “Tubeless” or “TL” label. Unlike “Tube Type”/”TT” tyres, any tyre so labelled is also operational without an inner tube. Models operational only with tubes are hardly to be found any more among modern passenger car and light truck tyres. At best, rare vintage cars and/or spoke wheel rims still need tubes.

Special labels: SSR, ContiSeal, MO and E
On increasingly popular run-flat tyres, the aforementioned labelling is followed by the “run-flat” designation. At Continental, this is “SSR” (Self Supporting Runflat Tyre). An SSR tyre has reinforced sidewalls and allows a vehicle to continue on its way even with a complete loss of tyre pressure. SSR tyres should be mounted only if the vehicle has a tyre pressure control system and was designed for such tyres by the manufacturer.

A tyre with ContiSeal technology continues to function even if its tread has been damaged by a nail or screw with a diameter of up to five millimetres.

This system makes it possible for a vehicle to still continue driving in around 80 per cent of all tyre punctures. The tyre has a viscous coating on the inner side of its tread that seals the tread puncture spot. Since this prevents any loss of air, ContiSeal tyres can also be mounted on vehicles without a tyre pressure control system.

Tyre manufacturers mark models that have been manufactured according to the specifications of vehicle manufacturers with MO, N0 - N4, a star, the letter “J“ or RO 1. These tyres differ slightly from tyres without the additional code. MO tyres, for example, are produced to Mercedes specifications, while Porsche-approved tyres are labelled N0 – N 4. Tyres approved by Jaguar are identifiable as such by a “J”. The tyres that BMW fits on the cars at its factories are identified by a small star. The designation “R01” can be found on tyres for Audi Quattro GmbH. Tyres with such identifiers can, however, also be fitted on other vehicles.

Of late, some Continental original equipment tyres have an “E" after the tread designation. Tyres so labelled are designed for especially low petrol consumption on these vehicles.

Tyre age
A DOT code is vulcanised into each tyre. This certifies compliance with the stipulations of the American Department of Transportation. In addition to a code for the manufacturer, the tyre size and tyre properties, the week of production is also shown in an encrypted form. The number 2208 means that the tyre was manufactured in the 22nd week of this year.

Two further alphanumeric combinations are still to be noted. “E4" is a mark of approval based on the EC Regulation. The number behind the “E" stands for the country issuing the approval (examples: 4 = the Netherlands, 12 = Austria). The number sequence “0214338” after “E4” is the approval number as per the applicable EC regulation. Even if the DOT code already tells experts the tyre’s country of origin, providers of quality products, such as Continental, vulcanise “Made in…” onto each tyre to identify the country of origin.