Tire code

Automotive tires are described by several alphanumeric tire codes (North American English spelling) or tyre codes (Commonwealth English spelling), which are generally molded into the sidewall of the tire. These codes specify the dimensions of the tire and its key limitations, such as load-bearing ability and maximum speed. Sometimes the inner sidewall contains information not included on the outer sidewall, and vice versa. The code has grown in complexity over the years, as is evident from the mix of SI and USC units, and ad-hoc extensions to lettering and numbering schemes. Most passenger car tires sizes are given using either the P Metric tire sizing system or the Metric tire sizing system (which is based on ISO standards but is not to be confused with the ISO metric system). Pickup trucks and SUVs use the Light Truck Numeric or Light Truck High Flotation system. Heavy trucks and commercial vehicles use another system altogether.

Automotive tires are described by several alphanumeric tire codes (North American English spelling) or tyre codes (Commonwealth English spelling), which are generally molded into the sidewall of the tire. These codes specify the dimensions of the tire and its key limitations, such as load-bearing ability and maximum speed. Sometimes the inner sidewall contains information not included on the outer sidewall, and vice versa. The code has grown in complexity over the years, as is evident from the mix of SI and USC units, and ad-hoc extensions to lettering and numbering schemes. Most passenger car tires sizes are given using either the P Metric tire sizing system or the Metric tire sizing system (which is based on ISO standards but is not to be confused with the ISO metric system). Pickup trucks and SUVs use the Light Truck Numeric or Light Truck High Flotation system. Heavy trucks and commercial vehicles use another system altogether. ===Vehicle class=== An optional letter (or letters) indicating the intended use or vehicle class for the tire: P: Passenger car LT: Light truck C: Commercial trucks ST: Special trailer M/C: Motorcycle T: Temporary (restricted usage for "space-saver" spare wheels) A preceding "P" indicates that the tire loads are designed to TRA standards, while the absence of a letter indicates that the tire conforms to ETRTO standards. ===Section width=== A 3-digit number indicating the "nominal section width" of the tire in millimeters; the widest point from both outer edges (side wall to side wall). The tire surface that touches the road usually has a narrower width (called "tread width"). ===Aspect ratio=== A 2- or 3-digit number indicating the "aspect ratio" of the sidewall height as a percentage of the nominal section width of the tire. If the information is omitted, it is assumed to be 82%. However, if the number is larger than 200, then this is the diameter of the entire tire in millimeters. ===Load index and load range=== The tyre load index (LI) on a passenger-car tire is a two- or three-digit numerical code used to cross-reference a load and inflation table that will give the maximum load each tire can carry at a given pressure. The load index is sometimes used in conjunction with the load range, which appears elsewhere on the tire. It usually consists of two letters (usually LL for Light Load, SL for Standard Load, and XL for Extra Load). However, it may also be written out as "EXTRA LOAD." It may also be absent entirely, which indicates a Standard Load tire. These two codes allow one to look up the required cold inflation pressure to carry a given load, according to the load inflation charts or tables. The load tables are too large to include in this article, but may be found at tirepressure.org. Generally, tire codes with a preceding "P" shall reference the P Metric Tire Load Inflation Chart, while those without shall reference the Metric Tire Load Inflation Chart. ===Load range=== The load range letter on light-truck tires indicates their ply rating. ==Wheel/rim widths== To determine the allowable range of rim widths for a specific tire size, the TRA Yearbook or the manufacturer's guide should always be consulted for that specific tire there is no rule of thumb. Running a tire on a rim size or type not approved by its manufacturer can result in tire failure and a loss of vehicle control. ==Additional marks== There are numerous other markings on a typical tire, these may include: "*": BMW-Mini original manufacturer fitment 030908: Approval number of the tire "100T": Commonly appears after tire size. Meaning: standard load inflation table (100) & speed rating (T) 3PMSF: or Three Peak Mountain Snow Flake, for tires rated for "severe snow" 3PMSF with Ш ("Sha"): or Three Peak Mountain Snow Flake, for studded tires rated for "severe snow" with the addition of the Cyrillic letter "Sha" (Ш), the first letter in the Russian word for studs or spikes (Шипы) AMx: Aston Martin OE Fitments "AO": Audi original manufacturer fitment Arrows: Some tread designs are "directional", and designed to perform better when driven in a specific direction. Such tires will have an arrow showing which way the tire should rotate when the vehicle is moving forwards. A/T or AT: All Terrain; Designed for all conditions on and off road, master of none B: Bias belted; tires for motorcycles (Example: 150/70 B 17 69 H) diagonal construction with belt added under the tread BSB: Broken serrated band BSL: Black serrated letters BSW: Black sidewall E4: Tire approved according to the ECE-regulations, the number indicating the country of approval. "ELT": Pirelli Elect tyres, specific for electric car IGS: or ice grip symbol, for tires rated for "ice conditions" "J": Jaguar original manufacturer fitment LL: Light load; tires for light usage and loads "M/C": Only for motorcycle fitment M+S, or M&S: Mud and snow; A tire that meets the Rubber Manufacturers Association (RMA) and Rubber Association of Canada (RAC) all-season tire definition. These are commonly found on all-season tires, with self-cleaning tread and average traction in muddy or very snowy conditions, and for low temperatures. M+SE: M+S tire with an additional "E" for extreme M+T or M&T: Mud and terrain; Designed to perform in mud or on other terrain that requires additional traction such as on rocks, in deeper snow, and in loose gravel. M/T or MT: Mud terrain; Designed for deep mud and rock crawl Made in ...: Country of production MGT: Maserati genuine tire. Original tires for Maserati MO: Original tires for Mercedes-Benz MOE: Mercedes-Benz Original Extended mobility (sometimes incorrectly referred to as a Run-flat tire) N-x: Original tires for Porsche where "x" is a "0" for the first approved in that size, "1" the second, ... "NHS": Not highway service ORWL: Outlined raised white lettering OWL: Outlined white lettering RF: Reinforced for Euro-metric tires, the term 'reinforced' means the same thing as 'extra load' RFT: Run-flat tire; Tires designed for vehicles without spare tires. Reinforced sidewalls allow the tire to be driven "flat" for a distance specified by the manufacturer (usually 50 miles) RSC (inside a circle): BMW runflat system component RWL: Raised white lettering SFI, or Inner: side facing inward; inside of asymmetric tires SFO, or Outer: side facing outward; outside of asymmetric tires SL: Standard load; tire for normal usage and loads (*): Original tires for BMW TL: Tubeless TPC: General Motors OE fitments TT: Tube-type, tire must be used with an inner-tube TWI: Tread wear indicator – a device, such as a triangle or a small Michelin Man icon, located where the tread meets the sidewall, and indicating the location of the raised wear bars in the tire tread channels – TWI is also used to refer to the raised wear bars themselves. VSB: Vertical serrated band WSW: White sidewall XL: extra load; a tire that allows a higher inflation pressure than a standard load tire, which increases the tire's maximum load ZP: zero-pressure; Michelin's branding for their run-flat models. To facilitate proper balancing, most tire manufacturers also mark red circles (uniformity) and/or yellow dots (weight) on the sidewalls of their tires to enable the best possible match-mounting of the tire/wheel assembly. ==Tire geometry== When referring to the purely geometrical data, a shortened form of the full notation is used. To take a common example, 195/55R16 would mean that the nominal width of the tire is approximately 195 mm at the widest point, the height of the sidewall of the tire is 55% of the width (107 mm in this example) and that the tire fits rims. The code gives a direct calculation of the theoretical diameter of the tire. For a size shown as "T/A_W" use (2×T×A/100) + (W×25.4) for a result in millimeters or (T*A/1270)+ W for a result in inches. Take the common example used above; (2×195×55/100)+(16×25.4) = 621 mm or (195×55/1270)+16 = 24.44 inches. Less commonly used in the US and Europe (but often in Japan for example) is a notation that indicates the full tire diameter instead of the aspect ratio of the side-wall height. To take the same example, a 16-inch rim would have a diameter of 406 mm. Adding twice the tire height (2×107 mm) makes a total 620 mm tire diameter. Hence, a 195/55R16 tire might alternatively be labelled 195/620R16. Whilst this is theoretically ambiguous, in practice these two notations may easily be distinguished because the height of the side-wall of an automotive tire is typically much less than the width. Hence when the height is expressed as a percentage of the width, it is almost always less than 100% (and certainly less than 200%). Conversely, vehicle tire diameters are always larger than 200 mm. Therefore, if the second number is more than 200, then it is almost certain the Japanese notation is being used if it is less than 200 then the U.S./European notation is being used. The diameters referred to above are the theoretical diameter of the tire. The actual diameter of a specific tire size can only be found in the TRA Yearbook or the manufacturer's data books. Note that the tire's cross-section and diameter are always specified when measured on a rim of a specified width; different widths will yield different tire dimensions. ===Examples=== The tires on a BMW Mini Cooper might be labeled: P195/55R16 85H P – these tires are for a passenger vehicle. However 'P' denotes P metric size load and speed rating changes for P tire & non-P tires 195 – the nominal width of the tire is approximately 195 mm at the widest point 55 – indicates that the height of the sidewall of the tire is 55% of the width (107 mm) R – this is a radial tire 16 – this tire fits rims 85 – the load index, a maximum of per tire in this case H – the speed index, this means the maximum permitted speed, here 210 km/h (130 mph) The tires on a Hummer H1 might be labeled: 37X12.5R17LT 37 – the tire is in diameter 12.5 – the tire has a cross section of R – this is a radial tire 17 – this tire fits rims LT – this is a light truck tire ==Historical tire codes== ==See also== Bicycle tire Motorcycle tyre Plus sizing Speedometer errors induced by variations in tire size. Tire manufacturing Uniform Tire Quality Grading (UTQG) Wheel sizing ==References== ==External links== List of DOT codes, Complete List of United States Tire DOT codes by manufacturer and plant , United States Department of Transportation UK Government bans tyres over 10 years, United Kingdom Department of Transport Tires Lifespan and Tire Sidewall Code for Load Index, Tires Book Tire Size Calculator and Conversion, Tirelib Tire Safety checks, Tyre Safety checks

Text derived from https://en.wikipedia.org/w/index.php?oldid=1372218653 under CC BY-SA 4.0; modifications have been made.