Tire code
Encyclopedia
Automobile
tire
s are described by an alphanumeric tire code (in American English
) or tyre code (in British English
, Australian English
and others), 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 metric and imperial units, and ad-hoc extensions to lettering and numbering schemes. New automotive tires frequently have ratings for traction, treadwear, and temperature resistance (collectively known as The Uniform Tire Quality Grade (UTQG) rating
s).
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.
(ETRTO) and the Tire and Rim Association (TRA) are two organizations that influence national tire standards. The objective 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.
Some light truck tires follow the Light Truck Numeric or Light Truck High Flotation systems, indicated by the letters LT at the end instead of the beginning of the sequence, as follows:
There is a common misconception that there is a specific equivalence between a tire's Load Range (or ply rating) and its inflation pressure at which it achieves its maximum load. In reality, tires of the same Load Index may require dramatically different pressures to achieve their published load ratings.
This can be seen by consulting the standards published every year by the industry standards group, the Tire and Rim Association. As an example, their 2010 Year Book shows that Load Range C tires may require 35 psi (241.3 kPa) or 55 psi (379.2 kPa), Load Range D tires may require 50 psi (344.7 kPa) or 65 psi (448.2 kPa), and Load Range E tires may require 65 psi (448.2 kPa) or 80 psi (551.6 kPa) to achieve their Load Index and Maximum Loads. This is also the case in the tables published by major tire makers, who do follow these TRA standards and have multiple inflation pressures for the same Load Range in the tires they sell.
It is essential to consult the guides like those just mentioned when making tire substitutions, and to read exactly what is imprinted on the sidewalls of tires. A different size of tire with the same Load Range may require a higher inflation pressure, and may fail in use if under-inflated.
While all ETRTO tires of the same load index will have the same maximum load P-Metric tires with the same load index may have different load capacities depending on the tire size. The TRA Inflation Tables must always be consulted when comparing the load capacity of P-Metric tires—the Load Index alone is not sufficient. An example: a P205/50R15 Standard Load tire has a load index of 84 and a load rating of 1113 lb (504.8 kg) at 35 psi (241.3 kPa). A P215/50R13 with the same load index of 84 only has a load rating of 1091 lb (494.9 kg), also at 35 psi (241.3 kPa).
ETRTO produces a Standards Manual (current edition 2010) which contains a number of specifications and tables. The load index table (2010 page G7) lists the Load index from 0–45 kg (0–99.2 lb) to 279–136000 kg (615.1–299,828.7 lb) (although it appears to relate to an inflation pressure of 42 psi (289.6 kPa) it doesn't specify, but see Load Inflation Table). The Load Inflation Table references the load index to inflation pressures between 22 psi (151.7 kPa) and 42 psi (289.6 kPa) at 1 psi (6.9 kPa) intervals which is too large to be included here.
Prior to 1991, tire speed ratings were shown inside the tire size, before the "R" construction type. The available codes were SR (112 mph, 180 km/h), HR (130 mph, 210 km/h), VR (in excess of 130 mph, 210 km/h).
Tires with a speed rating higher than 186 mph (300 km/h) are indicated by a Y in parenthesis. The load rating is often included within the parenthesis, e.g. (86Y).
In many countries, the law requires that tires must be specified, and fitted, to exceed the maximum speed of the vehicle they are mounted on, with regards to their speed rating code (except for "Temporary Use" spare tires). In the some parts of the European community, tires that are not fit for a car's or motorcycle's particular maximum speed are illegal to mount. The sole exception are M+S tires, where a warning sticker stating the allowed maximum speed must be placed within clear sight of the driver inside the vehicle. Some manufacturers will install a speed governor if a vehicle is ordered with tires rated below the vehicle's maximum speed.
If a tire is replaced with a lower speed rating than originally specified by the vehicle manufacturer, then this may render the vehicle insurance invalid.
. 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.
Less commonly used in the USA and Europe (but often in Japan for example) is a notation that indicates the full tire diameter instead of the side-wall height. To take the same example, a 16-inch wheel 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 wheel of a specified width; different widths will yield different tire dimensions.
The tires on a Hummer H1
might be labeled: 37X12.5R17LT
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
tire
Tire
A tire or tyre is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground...
s are described by an alphanumeric tire code (in American English
American English
American English is a set of dialects of the English language used mostly in the United States. Approximately two-thirds of the world's native speakers of English live in the United States....
) or tyre code (in British English
British English
British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...
, Australian English
Australian English
Australian English is the name given to the group of dialects spoken in Australia that form a major variety of the English language....
and others), 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 metric and imperial units, and ad-hoc extensions to lettering and numbering schemes. New automotive tires frequently have ratings for traction, treadwear, and temperature resistance (collectively known as The Uniform Tire Quality Grade (UTQG) rating
UTQG
UTQG stands for Uniform Tire Quality Grading.The National Highway Traffic Safety Administration established the Uniform Tire Quality Grading Standards in 49 CFR 575.104.- Treadwear :...
s).
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.
National technical standards regulations
The European Tyre and Rim Technical OrganisationEuropean Tyre and Rim Technical Organisation
The European Tyre and Rim Technical Organisation exists to specify and harmonise sizes of rims and their associated pneumatic tyres across the European Union. ETRTO sizes apply to rims for vehicles of all types, including bicycles...
(ETRTO) and the Tire and Rim Association (TRA) are two organizations that influence national tire standards. The objective 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.
Explanation of tire codes
The ISO Metric tire code consists of a string of letters and numbers, as follows:- An optional letter (or letters) indicating the intended use or vehicle class for the tire:-
- P: Passenger Car
- LT: Light Truck
- ST: Special Trailer
- T: Temporary (restricted usage for "Space-Saver" spare wheels)
-
- Use of the letter P indicates that the tire is engineered to TRA standards and absence of a letter indicates that the tire is engineered to ETRTO standards. In practice, the standards of the two organizations have evolved together and are virtually interchangable.
- 3 digit number: The "nominal section width" of the tire in millimeters; the widest point from both outer edges.
- /: Slash character for character separation.
- 2 or 3 digit number: The "aspect ratio" of the sidewall height to the total width of the tire, as a percentage. If the information is omitted, it is assumed to be 82%. If the number is larger than 200, then this is the diameter of the entire tire in millimeters.
- An optional letter indicating construction of the fabric carcass of the tire:
- B: bias belt (where the sidewalls are the same material as the tread, leading to a rigid ride)
- D: diagonal
- R: radialRadial tireA radial tire is a particular design of automotive tire . In this design, the cord plies are arranged at 90 degrees to the direction of travel, or radially ....
- if omitted, then it is a cross ply tire
- 2 digit number: Diameter in inches of the wheel that the tires are designed to fit. There is the rare exception metric diameter tires, such as the use of the 390 size, which in this case would indicate a wheel of 390 mm in diameter. Few tires are made to this size presently.
- 2 or 3 digit number: Load index; see table below
- 1 or 2 digit/letter combo: Speed rating; see table below
- Additional marks: See subheading below.
- Use of the letter P indicates that the tire is engineered to TRA standards and absence of a letter indicates that the tire is engineered to ETRTO standards. In practice, the standards of the two organizations have evolved together and are virtually interchangable.
Light trucks
- The tire diameter is given for High Flotation tires and omitted from Numeric tires.
- 2 digit number: The diameter of the tire in inches.
- x: Separator character.
- 3 or 4 digit number: The section width (cross section) of the tire in inches. If the tire diameter is not given, section widths ending in zero (e.g., 7.00 or 10.50) indicate the aspect ratio is 92%, while section widths not ending in zero (e.g., 7.05 or 10.55) indicate the aspect ratio is 82%.
- Construction of the fabric of the tire:
- B: bias belt
- D: diagonal
- R: radial
- 2 digit number: Diameter in inches of the wheel rim that this tire is designed to fit.
- LT: Designates that this is a Light Truck tire.
- Load index and speed rating are not required for this type of tire but may be provided by the manufacturer.
- 2 or 3 digit number: Load index; see table below.
- 1 or 2 digit/letter combination: Speed rating; see table below.
- Additional marks: See subheading below.
Load range
The Load Range Letter on light truck tires indicates their ply rating.| Load Range | Ply Rating |
|---|---|
| A | 2 |
| B | 4 |
| C | 6 |
| D | 8 |
| E | 10 |
| F | 12 |
| G | 14 |
| H | 16 |
| J | 18 |
| L | 20 |
| M | 22 |
| N | 24 |
There is a common misconception that there is a specific equivalence between a tire's Load Range (or ply rating) and its inflation pressure at which it achieves its maximum load. In reality, tires of the same Load Index may require dramatically different pressures to achieve their published load ratings.
This can be seen by consulting the standards published every year by the industry standards group, the Tire and Rim Association. As an example, their 2010 Year Book shows that Load Range C tires may require 35 psi (241.3 kPa) or 55 psi (379.2 kPa), Load Range D tires may require 50 psi (344.7 kPa) or 65 psi (448.2 kPa), and Load Range E tires may require 65 psi (448.2 kPa) or 80 psi (551.6 kPa) to achieve their Load Index and Maximum Loads. This is also the case in the tables published by major tire makers, who do follow these TRA standards and have multiple inflation pressures for the same Load Range in the tires they sell.
It is essential to consult the guides like those just mentioned when making tire substitutions, and to read exactly what is imprinted on the sidewalls of tires. A different size of tire with the same Load Range may require a higher inflation pressure, and may fail in use if under-inflated.
Load index
The load index on a passenger car tire is a numerical code stipulating the maximum load (mass, or weight) each tire can carry. For Load Range "B" tires, ETRTO (ISO-Metric) standards specify the load index rating at an inflation pressure of 36 psi (248.2 kPa) (table Below) while P-Metric standards measure the load capacity at an inflation pressure of 35 psi (241.3 kPa). The two standards vary slightly with the capacity required for different inflation pressures.While all ETRTO tires of the same load index will have the same maximum load P-Metric tires with the same load index may have different load capacities depending on the tire size. The TRA Inflation Tables must always be consulted when comparing the load capacity of P-Metric tires—the Load Index alone is not sufficient. An example: a P205/50R15 Standard Load tire has a load index of 84 and a load rating of 1113 lb (504.8 kg) at 35 psi (241.3 kPa). A P215/50R13 with the same load index of 84 only has a load rating of 1091 lb (494.9 kg), also at 35 psi (241.3 kPa).
ETRTO produces a Standards Manual (current edition 2010) which contains a number of specifications and tables. The load index table (2010 page G7) lists the Load index from 0–45 kg (0–99.2 lb) to 279–136000 kg (615.1–299,828.7 lb) (although it appears to relate to an inflation pressure of 42 psi (289.6 kPa) it doesn't specify, but see Load Inflation Table). The Load Inflation Table references the load index to inflation pressures between 22 psi (151.7 kPa) and 42 psi (289.6 kPa) at 1 psi (6.9 kPa) intervals which is too large to be included here.
| Code | Weight | Code | Weight | Code | Weight | Code | Weight | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| 60 | 250 kg (551.2 lb) | 80 | 450 kg (992.1 lb) | 100 | 800 kg (1,763.7 lb) | 120 | 1400 kg (3,086.5 lb) | ||||
| 61 | 257 kg (566.6 lb) | 81 | 462 kg (1,018.5 lb) | 101 | 825 kg (1,818.8 lb) | 121 | 1450 kg (3,196.7 lb) | ||||
| 62 | 265 kg (584.2 lb) | 82 | 475 kg (1,047.2 lb) | 102 | 850 kg (1,873.9 lb) | 122 | 1500 kg (3,306.9 lb) | ||||
| 63 | 272 kg (599.7 lb) | 83 | 487 kg (1,073.7 lb) | 103 | 875 kg (1,929 lb) | 123 | 1550 kg (3,417.2 lb) | ||||
| 64 | 280 kg (617.3 lb) | 84 | 500 kg (1,102.3 lb) | 104 | 900 kg (1,984.2 lb) | 124 | 1600 kg (3,527.4 lb) | ||||
| 65 | 290 kg (639.3 lb) | 85 | 515 kg (1,135.4 lb) | 105 | 925 kg (2,039.3 lb) | 125 | 1650 kg (3,637.6 lb) | ||||
| 66 | 300 kg (661.4 lb) | 86 | 530 kg (1,168.4 lb) | 106 | 950 kg (2,094.4 lb) | ||||||
| 67 | 307 kg (676.8 lb) | 87 | 545 kg (1,201.5 lb) | 107 | 975 kg (2,149.5 lb) | ||||||
| 68 | 315 kg (694.5 lb) | 88 | 560 kg (1,234.6 lb) | 108 | 1000 kg (2,204.6 lb) | ||||||
| 69 | 325 kg (716.5 lb) | 89 | 580 kg (1,278.7 lb) | 109 | 1030 kg (2,270.8 lb) | ||||||
| 70 | 335 kg (738.5 lb) | 90 | 600 kg (1,322.8 lb) | 110 | 1060 kg (2,336.9 lb) | ||||||
| 71 | 345 kg (760.6 lb) | 91 | 615 kg (1,355.8 lb) | 111 | 1090 kg (2,403 lb) | ||||||
| 72 | 355 kg (782.6 lb) | 92 | 630 kg (1,388.9 lb) | 112 | 1120 kg (2,469.2 lb) | ||||||
| 73 | 365 kg (804.7 lb) | 93 | 650 kg (1,433 lb) | 113 | 1150 kg (2,535.3 lb) | ||||||
| 74 | 375 kg (826.7 lb) | 94 | 670 kg (1,477.1 lb) | 114 | 1180 kg (2,601.5 lb) | ||||||
| 75 | 387 kg (853.2 lb) | 95 | 690 kg (1,521.2 lb) | 115 | 1215 kg (2,678.6 lb) | ||||||
| 76 | 400 kg (881.8 lb) | 96 | 710 kg (1,565.3 lb) | 116 | 1250 kg (2,755.8 lb) | ||||||
| 77 | 412 kg (908.3 lb) | 97 | 730 kg (1,609.4 lb) | 117 | 1285 kg (2,832.9 lb) | ||||||
| 78 | 425 kg (937 lb) | 98 | 750 kg (1,653.5 lb) | 118 | 1320 kg (2,910.1 lb) | ||||||
| 79 | 437 kg (963.4 lb) | 99 | 775 kg (1,708.6 lb) | 119 | 1360 kg (2,998.3 lb) |
Speed rating
The speed symbol is made up of a single letter or an A with one number. It indicates the maximum speed at which the tire can carry a load corresponding to its Load Index.| Code | mph | km/h | Code | mph | km/h | |
|---|---|---|---|---|---|---|
| A1 | 3 | 5 | L | 75 | 120 | |
| A2 | 6 | 10 | M | 81 | 130 | |
| A3 | 9 | 15 | N | 87 | 140 | |
| A4 | 12 | 20 | P | 94 | 150 | |
| A5 | 16 | 25 | Q | 100 | 160 | |
| A6 | 19 | 30 | R | 106 | 170 | |
| A7 | 22 | 35 | S | 112 | 180 | |
| A8 | 25 | 40 | T | 118 | 190 | |
| B | 31 | 50 | U | 124 | 200 | |
| C | 37 | 60 | H | 130 | 210 | |
| D | 40 | 65 | V | 149 | 240 | |
| E | 43 | 70 | Z | over 149 | over 240 | |
| F | 50 | 80 | W | 168 | 270 | |
| G | 56 | 90 | (W) | over 168 | over 270 | |
| J | 62 | 100 | Y | 186 | 300 | |
| K | 68 | 110 | (Y) | over 186 | over 300 |
Prior to 1991, tire speed ratings were shown inside the tire size, before the "R" construction type. The available codes were SR (112 mph, 180 km/h), HR (130 mph, 210 km/h), VR (in excess of 130 mph, 210 km/h).
Tires with a speed rating higher than 186 mph (300 km/h) are indicated by a Y in parenthesis. The load rating is often included within the parenthesis, e.g. (86Y).
In many countries, the law requires that tires must be specified, and fitted, to exceed the maximum speed of the vehicle they are mounted on, with regards to their speed rating code (except for "Temporary Use" spare tires). In the some parts of the European community, tires that are not fit for a car's or motorcycle's particular maximum speed are illegal to mount. The sole exception are M+S tires, where a warning sticker stating the allowed maximum speed must be placed within clear sight of the driver inside the vehicle. Some manufacturers will install a speed governor if a vehicle is ordered with tires rated below the vehicle's maximum speed.
If a tire is replaced with a lower speed rating than originally specified by the vehicle manufacturer, then this may render the vehicle insurance invalid.
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 thumbRule of thumb
A rule of thumb is a principle with broad application that is not intended to be strictly accurate or reliable for every situation. It is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination...
. 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:- 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 all-weather tires, with self-cleaning tread and above-average traction in muddy or very light snowy conditions, and for low ambient temperatures. Spike tires have an additional letter, "E" (M+SE).
- Mountain Snowflake Pictograph: Winter passenger and light truck tires that meet the severe snow service requirements of Rubber Manufacturers Association (RMA) and Rubber Association of Canada (RAC).
- BSW: Black SideWall
- WSW: White SideWall
- OWL: Outline White Lettering
- RWL: Raised White Lettering
- VSB: Vertical Serrated Band
- BSL: Black Serrated Letters
- E4: Tire approved according ECE-regulations, the number indicating the country of approval.
- 030908: Approval number of the tire
- DOT code: All tires for use in the USA have the DOT code, as required by the Department of TransportationUnited States Department of TransportationThe United States Department of Transportation is a federal Cabinet department of the United States government concerned with transportation. It was established by an act of Congress on October 15, 1966, and began operation on April 1, 1967...
(DOT). It specifies the company, factory, mold, batch, and date of production (two digits for week of the year plus two digits for year; or two digits for week of the year plus one digit for year for tires made prior to 2000). Although not law, some tire manufacturers do not suggest using a "new" tire that has been sitting on the shelf for more than six years (Ford Motor Company) or 10 years (Cooper Tire citing a tire association recommendation). JATMA, the Japanese Automotive Tyre Manufacturers Association recommends that all tires be inspected at five years, and all tires that were manufactured more than ten years previous be replaced. - TL: Tubeless
- TT: Tube-type, tire must be used with an inner-tube
- Made in ...: Country of production
- C: Commercial; tires for light trucks (Example: 185 R14 C)
- B: Bias belted; tires for motorcycles (Example: 150/70 B 17 69 H)—diagonal construction with belt added under the tread
- SFI, or Inner: Side Facing Inwards; inside of asymmetric tires
- SFO, or Outer: Side Facing Outwards; outside of asymmetric tires
- TWI: Tread Wear Indicator; a device, such as a triangle or a small Michelin Man icon, located where the tread meets the sidewall. It indicates the location of the raised wear bars in between the tire tread channels.
- LL: Light Load; tires for light usage and loads
- SL: Standard Load; tire for normal usage and loads
- XL: eXtra Load; a tire that allows a higher inflation pressure than a Standard Load tire, which increases the tire's maximum load
- RF: Reinforced -- for Euro-metric tires, the term 'reinforced' manes the same thing as 'Extra Load'
- Arrows: Some tread designs are "directional", and designed to perform better when driven in a specific direction (clockwise or counter-clockwise). Such tires will have an arrow showing which way the tire should rotate when the vehicle is moving forwards. It is important not to put a "clockwise" tire on the left hand side of the car or a "counter-clockwise" tire on the right side.
- MO: Original tires for Mercedes-BenzMercedes-BenzMercedes-Benz is a German manufacturer of automobiles, buses, coaches, and trucks. Mercedes-Benz is a division of its parent company, Daimler AG...
- MOE: Mercedes-BenzMercedes-BenzMercedes-Benz is a German manufacturer of automobiles, buses, coaches, and trucks. Mercedes-Benz is a division of its parent company, Daimler AG...
Original Extended - N-x: Original tires for PorschePorschePorsche Automobil Holding SE, usually shortened to Porsche SE a Societas Europaea or European Public Company, is a German based holding company with investments in the automotive industry....
where "x" is a "0" for the first approved in that size, "1" the second, ... - Star: Original tires for BMWBMWBayerische Motoren Werke AG is a German automobile, motorcycle and engine manufacturing company founded in 1916. It also owns and produces the Mini marque, and is the parent company of Rolls-Royce Motor Cars. BMW produces motorcycles under BMW Motorrad and Husqvarna brands...
- RSC in a Circle: BMWBMWBayerische Motoren Werke AG is a German automobile, motorcycle and engine manufacturing company founded in 1916. It also owns and produces the Mini marque, and is the parent company of Rolls-Royce Motor Cars. BMW produces motorcycles under BMW Motorrad and Husqvarna brands...
Runflat System Component - TPC: General MotorsGeneral MotorsGeneral Motors Company , commonly known as GM, formerly incorporated as General Motors Corporation, is an American multinational automotive corporation headquartered in Detroit, Michigan and the world's second-largest automaker in 2010...
OE Fitments - AMx: Aston MartinAston MartinAston Martin Lagonda Limited is a British manufacturer of luxury sports cars, based in Gaydon, Warwickshire. The company name is derived from the name of one of the company's founders, Lionel Martin, and from the Aston Hill speed hillclimb near Aston Clinton in Buckinghamshire...
OE Fitments - "100T": Commonly appears after tire size. Meaning: Standard Load Inflation Table (100) & Speed Rating (T)
- 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 side-wall of the tire is 55% of the width (107 mm in this example) and that the tire fits 16 inches (406.4 mm) wheels. 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 USA and Europe (but often in Japan for example) is a notation that indicates the full tire diameter instead of the side-wall height. To take the same example, a 16-inch wheel 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 wheel 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 16 in (406.4 mm) wheels
- 85 — the load index, a maximum of 515 kg (1,135.4 lb) 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
Hummer H1
The Hummer H1 is a civilian off-road vehicle based on the M998 Humvee, which was created by AM General. The vehicle was produced from 1992 through 2006, and was the first of what became the Hummer line...
might be labeled: 37X12.5R17LT
- 37 - the tire is 37 in (939.8 mm) in diameter
- 12.5 - the tire has a cross section of 12.5 in (317.5 mm)
- R - this is a radial tire
- 17 - this tire fits 17 in (431.8 mm) wheels
- LT - this is a light truck tire.
Tractor tires
The numeric codes on tractor tires since 1955 have required either two or three numbers: W-D or H/W-D where 'W' is the width of the tire in inches, D is the diameter of the rim in inches and H (if provided) is the percentage height of the tire. Hence, 5.00-15 is a tire that will fit a 15 inches (381 mm) rim and is 5 in (127 mm) wide but of indeterminate height. 25/5-16 is a tire that has a 5 in (127 mm) width, fits a 16 inches (406.4 mm) rim and whose height is approximately 25 in (635 mm).See also
- Motorcycle tiresMotorcycle tyresMotorcycle tyres provide the only contact with the ground, via the contact patch under normal conditions, and so have a very large influence over motorcycle handling characteristics. Motorcycle tyres have a round cross section to facilitate the leaning necessary when a motorcycle turns...
- Plus sizing
- Speedometer errors induced by variations in tire size.
- Tire manufacturingTire manufacturingPneumatic tires are manufactured according to relatively standardized processes and machinery, in around 450 tire factories in the world. With over 1 billion tires manufactured worldwide annually, the tire industry is the major consumer of natural rubber...
- Uniform Tire Quality Grading (UTQG)UTQGUTQG stands for Uniform Tire Quality Grading.The National Highway Traffic Safety Administration established the Uniform Tire Quality Grading Standards in 49 CFR 575.104.- Treadwear :...
- Wheel sizingWheel sizingThe wheel size for a motor vehicle or similar wheel has a number of parameters.-Bolt pattern:The bolt pattern is the number of lug nuts or wheel studs on the wheel hub. As the bolts are most often evenly spaced, the number of bolts determines the pattern. For example: smaller cars have three...