Шина өлшемдері мен белгілеу кодексі

Alphanumeric code specifying tire sizes and limits

Automotive tires are described by an alphanumeric tire code (in North American English) or tyre code (in Commonwealth English), which is generally molded into the sidewall of the tire. This code specifies the dimensions of the tire, and some of 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. New automotive tires frequently have ratings for traction, treadwear, and temperature resistance, all collectively known as the Uniform Tire Quality Grading. Most tires sizes are given using the ISO metric sizing system. However, some pickup trucks and SUVs use the Light Truck Numeric or Light Truck High Flotation system.

The DOT code is an alphanumeric character sequence molded into the sidewall of the tire and allows the identification of the tire and its age. The code is mandated by the U. S. Department of Transportation but is used worldwide. The DOT code is also useful in identifying tires subject to product recall or at end of life due to age. Since February 2021 UK vehicle Regulations do not permit the use of tyres over 10 years old on the front steered axle(s) of heavy goods vehicles, buses and coaches. The ban also applies to all tyres in single configuration on minibuses. In addition, it is a requirement for all tyres on these vehicles to display a legible date code.

The European Tyre and Rim Technical Organisation (ETRTO) and the Tire and Rim Association (TRA) are two organizations that influence national tire standards. The objectives of the ETRTO include aligning national tire and rim standards in Europe. The Tire and Rim Association, formerly known as The Tire and Rim Association of America, Inc., is an American trade organization which standardizes technical standards. In the United States, the Office of Vehicle Safety Compliance, a component of the Department of Transportation, is one of the agencies tasked to enforce the Federal Motor Vehicle Safety Standard (FMVSS). Canada has published tire regulations, such as the Motor Vehicle Tire Safety Regulations SOR 95 148.

All tires sold for road use in Europe after July 1997 must carry an E mark. The mark itself is either an upper case "E" or lower case "e" – followed by a number in a circle or rectangle, followed by a further number. An (upper case) "E" indicates that the tire is certified to comply with the dimensional, performance and marking requirements of ECE Regulation 30. A (lower case) "e" indicates that the tire is certified to comply with the dimensional, performance and marking requirements of Directive 92/23/EEC. The number in the circle or rectangle denotes the country code of the government that granted the type approval. The last number outside the circle or rectangle is the number of the type approval certificate issued for that particular tire size and type.

The speed symbol is made up of a single letter or an A with one numeral. It indicates the maximum speed at which the tire can carry a load corresponding to its load index. In this case it is possible to calculate the appropriate speed rating with a formula. Tires with a higher speed rating generally have a better grip but a lower tread life, reduced performance in cold weather and reduced driving comfort.

The treadwear is a 3 digit comparative rating. It is part of Uniform Tire Quality Grading standard.

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 tirethere 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.

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 side wall 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 usedif 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.

Prior to 1964, tires were all made to a 90% aspect ratio. Tire size was specified as the tire width in inches and the diameter in inches – for example, 6.50 15. From 1965 to the early 1970s, tires were made to an 80% aspect ratio. Tire size was again specified by width in inches and diameter in inches. To differentiate from the earlier 90 ratio tires, the decimal point is usually omitted from the width – for example, 685 15 for a tire 6.85 inches wide. Starting in 1972 tires were specified by load rating, using a letter code. In practice, a higher load rating tire was also a wider tire. In this system a tire had a letter, optionally followed by "R" for radial tires, followed by the aspect ratio, a dash and the diameter – C78 15 or CR78 15 for bias and radial, respectively. Each diameter of rim had a separate sequence of load ratings; thus, a C78 14 and a C78 15 are not the same width. An aspect ratio of 78% was typical for letter sized tires, although 70% was also common and lower profiles down to 50% were occasionally seen.