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Understanding tire sidewall information
What does 205/55 R 16 91 V actually mean? Continental Tire Canada explains information on the tire sidewall
A tire sidewall contains several alphanumerical codes. Some of them help the manufacturer or tire dealer to identify the products; others give information on the tire’s size, type, maximum permissible speed and load rating. Recently information relevant to original equipment on run-flat properties and low rolling resistance has been added.
Size and type
Although the label “205/55 R16 91V" doesn't say much to the tire layman, it is really rather simple. “205" specifies the tire’s nominal width in millimetres. The number “55" refers to the nominal aspect ratio, i.e. the ratio of the tire’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 tires, 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 tires, which were previously the norm. For these reasons diagonal passenger tires have not been mass-produced in Europe for more than 30 years now. They are still available, however, for utility vehicles and as special tires for extreme off-road use. Their casing cords run over the tires 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 tire’s load index (LI). There is a standard conversion table for converting this numerical code to the maximum tire 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 tire can be loaded with a maximum of 615 kilograms. The speed symbol “V” – indicating the tire’s speed rating – is indicated right after load rating “91”. In this case, the tire 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) tires is not standardized. Confirmation from the tire manufacturer is therefore required for speeds in excess of 240 km/h. Together a tire’s load index and speed index constitute the passenger tire’s service description.
Only approved winter tires have the “snowflake on the mountain” symbol
Road user safety is the number one priority of Continental’s tire developers. That is why Continental offers both summer and winter tires. Each tire type optimally ensures high safety requirements only in the appropriate season. A genuine winter tire is easy to identify from the numerous sipes on the tire 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 tire. Tires that bear this symbol have been tested against a reference tire to demonstrate their winter suitability. Continental therefore strongly advises customers to keep an eye out for this additional label when buying winter tires.
Safe tread depth
The abbreviation “TWI“ stands for tread wear indicator. Crossbars are evenly distributed in the main circumferential grooves over the tire circumference. When the legally defined minimum tread depth of 2/32nds (= 1.6 mm) is reached, the crossbars are flush with the tread blocks. Numerous tests in Europe conducted by leading car magazines and tests performed by Continental itself prove that the safety reserves of summer tires under wet conditions significantly decrease with a residual tread depth of less than three millimetres. A raindrop on the sidewall of new Continental summer tires indicates the minimum tread depth recommended by Continental for driving under wet conditions. In the case of winter tires, 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.
“TL” stands for tubeless tires
A closer look at the tire also reveals a “Tubeless” or “TL” label. Unlike “Tube Type”/”TT” tires, any tire 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 tires. 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 tires, the aforementioned labelling is followed by the “run-flat” designation. At Continental, this is “SSR” (Self Supporting Runflat Tire). An SSR tire has reinforced sidewalls and allows a vehicle to continue on its way even with a complete loss of tire pressure. SSR tires should be mounted only if the vehicle has a tire pressure control system and was designed for such tires by the manufacturer.
A tire 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 tire punctures. The tire 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 tires can also be mounted on vehicles without a tire pressure control system.
Tire 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 tires differ slightly from tires without the additional code. MO tires, for example, are produced to Mercedes specifications, while Porsche-approved tires are labelled N0 – N 4. Tires approved by Jaguar are identifiable as such by a “J”. The tires that BMW fits on the cars at its factories are identified by a small star. The designation “R01” can be found on tires for Audi Quattro GmbH. Tires with such identifiers can, however, also be fitted on other vehicles.
Of late, some Continental original equipment tires have an “E" after the tread designation. Tires so labelled are designed for especially low petrol consumption on these vehicles.
A DOT code is vulcanized into each tire. This certifies compliance with the stipulations of the American Department of Transportation. In addition to a code for the manufacturer, the tire size and tire properties, the week of production is also shown in an encrypted form. The number 2208 means that the tire was manufactured in the 22nd week of 2008.
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 tire’s country of origin, providers of quality products, such as Continental, vulcanize “Made in…” onto each tire to identify the country of origin.
Posted Sept. 12, 2008. © CarTest.ca.