Tire code explained

Automotive tires are described by several alphanumeric tire codes (in North American English) or tyre codes (in Commonwealth English), 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.

ETRTO, TRA, and JATMA

The European Tyre and Rim Technical Organisation (ETRTO) and the Tire and Rim Association (TRA), formerly known as The Tire and Rim Association of America, Inc.,[1] are two organizations that influence national tire standards. There exists also the Japan Automobile Tyre Manufacturers' Association, Inc. (JATMA). In practice, the standards of the three organizations have evolved together and are fairly interchangeable, though the load and inflation tables will give slightly different values for the same size tire.[2]

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).[3] Canada has published tire regulations, such as the Motor Vehicle Tire Safety Regulations SOR 95-148.[4]

Metric tire codes

The metric tire code consists of a string of letters and numbers describing the dimensions of the tire, as follows:[5] [6]

Vehicle class

An optional letter (or letters) indicating the intended use or vehicle class for the tire:

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").

Slash

A slash "/" character for character separation.

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.

Construction

An optional letter or two indicating construction of the fabric carcass of the tire:

Diameter

A 1- or 2-digit number indicating the diameter, in inches, of the rim that the tires are designed to fit. There is the rare exception of metric-diameter tires, such as the use of the 390 size, which in this case would indicate a rim of 390 mm in diameter. Few tires are made to this size currently. The number may be longer where a half-inch size is used, for example many heavy transport trucks now use 22.5-inch tires.[7] [8]

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.[9] 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.

Tyre load index (LI) table[10] [11] [12] [13] [14] !Load index (LI)!kg!lbs!!Load index (LI)!kg!lbs!!Load index (LI)!kg!lbs
0459910080017642001400030900
146.510210182518192011450032000
247.510510285018742021500033100
348.710710387519292031550034200
45011010490019842041600035300
551.511410592520392051650036400
65311710695020942061700037500
754.512010797521492071750038600
856123108100022052081800039700
958128109103022712091850040800
1060132110106023372101900041900
1161.5136111109024032111950043000
1263139112112024692122000044100
1365143113115025352132060045400
1467148114118026012142120046700
1569152115121526792152180048100
1671157116125027562162240049400
1773161117128528332172300050700
1875165118132029102182360052000
1977.5171119136029982192430053600
2080176120140030862202500055100
2182.5182121145031972212575056800
2285187122150033072222650058400
2387.5193123155034172232725060100
2490198124160035272242800061700
Load index (LI)kglbsLoad index (LI)kglbsLoad index (LI)kglbs
2592.5204125165036382252900063900
2695209126170037482263000066100
2797.5215127175038582273075067800
28100220128180039682283150069400
29103227129185040792293250071700
30106234130190041892303350073900
31109240131195042892313450076100
32112247132200044092323550078264
33115254133206045412333650080469
34118260134212046742343750082673
35121267135218048062353875085429
36125276136224049382364000088185
37128282137230050712374125090941
38132291138236052032384250093696
39136300139243053572394375096452
40140309140250055122404500099208
411453201412575567724146250101964
421503311422650584224247500104719
431553421432725600824348750107475
441603531442800617324450000110231
451653641452900639324551500113538
461703751463000661424653000116845
471753861473075677924754500120152
481803971483150684424856000123459
491854081493250716524958000127868
Load index (LI)kglbsLoad index (LI)kglbsLoad index (LI)kglbs
501904191503350739025060000132300
511954301513450761025161500135580
522004411523550783025263000138890
532064541533650805025365000143300
542124671543750827025467000147710
552184811553875854025569000152120
562244941564000882025671000156530
572305071574125909025773000160930
582365201584250937025875000165340
592435361594375965025977500170660
602505511604500992026080000176400
6125756716146251020026182500181880
6226558416247501050026285000187390
6327260016348751070026387500192900
6428061716450001100026490000198450
6529063916551501140026592500203920
6630063916653001170026695000209440
6730767716754501200026797500214950
68315694168560012300268100000220500
69325716169580012800269103000227370
70335739170600013200270106000233730
71345761171615013600271109000240345
72355783172630013900272112000246960
73365805173650014300273115000253575
74375827174670014800274118000260190
Load index (LI)kglbsLoad index (LI)kglbsLoad index (LI)kglbs
75387852175690015200275121000266805
76400882176710015700276125000275625
77412908177730016100277128500283343
78425937178750016500278132000291060
79437963179775017100279136000299880
80450992180800017600
814621019181825018200
824751047182850018700
834871074183875619300
845001102184900019800
855151135185925020400
865301168186950020900
875451201187975021500
8856012351881000022000
8958012791891030022700
9060013231901060023400
9161513561911090024000
9263013891921120024700
9365014331931150025400
9467014771941180026000
9569015211951215026800
9671015651961250027600
9773016091971285028300
9875016531981320029100
9977517091991360030000

Speed rating

The speed symbol or tyre speed index (SI) is made up of a single letter, or an A with one numeral. It is indicative of the maximum speed at which the tire can carry its rated load while ensuring that no part of the tire overheats when operating in steady-state conditions on smooth roads.

Speed rating
Codekm/hmphCodekm/hmph
A153L12075
A2106M13081
A3159N14087
A42012P15094
A52516Q160100
A63019R170106
A73522S180112
A84025T190118
B5031U200124
C6037H210130
D6540V240149
E7043Zover 240over 149
F8050W270168
G9056(W)over 270over 168
J10062Y300186
K11068(Y)over 300over 186

Speed ratings of S and above have certain constraints that must be met in order to reach their maximum speeds. Namely, their operating pressures must be adjusted according to the table below.

Speed ratingMax speed S1 without pressure adjustment (km/h)Pressure adjustment for every 10 km/h over S1 (kPa)Maximum speed S2 without load reduction (km/h)Load reduction for every 10 km/h over S2 (kg)Maximum speed (km/h)
S16051800%180
T16071900%190
H16062100%210
V16062103%240
W190102405%270
Y220102705%300
Speed ratings with parentheses such as (W) and (Y) have maximum speeds set by the manufacturers. The load rating is often included within the parentheses, e.g. (86Y).

Prior to 1991, tire speed ratings were shown inside the tire size, before the "R" construction type. The available codes were SR (180 km/h, 112 mph), HR (210 km/h, 130 mph), VR (in excess of 210 km/h, 130 mph), and ZR (in excess of 240 km/h, 150 mph).

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 some parts of the European Union, 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. In some parts of the European Union, e.g. Germany, it is allowed to mount tires with a lower speed rating code if the car manufacturer specifies tires with a very high speed rating in the registration documents and the vehicle will not reach this speed based on insufficient power.[15] In this case it is possible to calculate the appropriate speed rating with a formula.[16]

Other codes

Wear, traction, and temperature grades

The wear, traction, and temperature characteristics of passenger tires are displayed according to the Uniform Tire Quality Grading (UTQG) standard.

Date of Manufacture

At the end of the Tire Identification Number (TIN), a long string of letters and number encased in a long oval, are four numbers to indicate when the tire was made. The first two represent the week and the last two the year, so a TIN ending in "0422" indicates the tire was made in the 4th week (end of January) of 2022. Prior to 2000 only three digits were used so "042" could represent the 4th week of 1992, 1982, or earlier.[17]

Winter, Snow, and Ice Markings

See main article: Snow tires. Tires designed for use in snowy conditions display the appropriate lettering and marks to indicate its use for "(Mud and) Snow", "Severe Snow" (3PMSF), "Ice Conditions" (IGS) along with preceding and prerequisite indicators. Studded tires are similar, with pictograms incorporating the Cyrillic letter "Sha" (Π¨), the first letter in the Russian word for studs (Π¨ΠΈΠΏΡ‹), being standardized in 2022.

DOT code

The DOT code can be found immediately after the letters "DOT" on a tire sidewall.

It is useful in identifying tires subject to product recall[18] or at end of life due to age. It is mandated by the U.S. Department of Transportation[19] but is used worldwide.[20]

The first three characters indicate the manufacturing plant and are assigned by the NHTSA[21] (tires made before 2015 had only two characters).

Following the manufacturer's plant code, the next two digits within a DOT code signify the tire size. For instance, the size code "WC" might correspond to the tire size 205/55 R16. However, these size codes aren't standardized. Each tire manufacturer may assign these codes as they see fit, provided they maintain a consistent and explainable system within their coding.

After the size code, the next sequence in a DOT number consists of three or four digits that designate the tire type. This coding, though optional, is widely used by tire manufacturers for internal tracking purposes, such as managing returns and quality control. The decision on how exactly to code the tire type lies with each manufacturer, leading to a variety of coding systems across the industry.

The last four numbers of the DOT marking on tires tell you the week (1 through 53, according to ISO 8601) and year the tire was made. So, a tire with the last four digits of 0121 was made the first week of January 2021, 0221 is second week of January of 2021, and so on.

E-mark

All tires sold for road use in Europe after July 1997 must carry an E-mark.

Items type-approved according to a UN Regulation are marked with an E and the country's Distinguishing Number, within a circle. A capital (E) in a circle[22] indicates compliance with UN regulation 30, while a lower case [e] in a box indicates compliance with a EU directive (e.g. issued by EC, EU)[23] [24] . This number indicates which country approved the item, and other surrounding letters and digits indicate the precise version of the regulation met and the type approval number, respectively. A (lower case) "e" indicates that the tire is certified to comply with the dimensional, performance and marking requirements of Directive 92/23/EEC.[25]

Light truck (LT) tire codes

Flotation tires keep vehicle tires floating above loosely packed dirt, minimizing soil disturbance in agricultural environments and maximizing vehicle stability on unpaved surfaces in construction environments.

Light truck tires are indicated by the letters LT at the end instead of the beginning of the sequence, as follows:

As an example, if a tire size has two sets of numbers (6-12, 5.00-15, 11.2-24), then the first number (5.00-15) is the approximate width in inches, and the second number (5.00-15) is the rim diameter in inches.

If a tire size has three sets of numbers (15x6.00-6, 26x12.00-12, 31x15.50-15), then the first number (26x12.00-12) is the approximate tire diameter in inches, the second number (26x12.00-12) is the approximate width in inches, and the third number (26x12.00-12) is the rim diameter in inches.[26]

Load range

The load range letter on light-truck tires indicates their ply rating.[27]

Load rangePly rating
A2
B4
C6
D8
E10
F12
G14
H16
J18
L20
M22
N24

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 tirethere is no rule of thumb.[28] 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:

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 16adj=midNaNadj=mid rims. The code gives a direct calculation of the theoretical diameter of the tire. For a size shown as "T/A_W" use (2Γ—TΓ—A/100) + (WΓ—25.4) for a result in millimeters or (T*A/1270)+ W for a result in inches. Take the common example used above; (2Γ—195Γ—55/100)+(16Γ—25.4) = 621 mm or (195Γ—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 (2Γ—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.[33] 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

The tires on a Hummer H1 might be labeled: 37X12.5R17LT

Historical tire codes

North America

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 β€“ for example, 6.50-15.[34]

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 β€“ 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 β€“ 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.[35]

See also

External links

Notes and References

  1. http://www.us-tra.org/traAbout.html Scope of the Association and Some of its History
  2. http://www.dunloptires.com/care/tech.html Care and Maintenance - Technical
  3. http://www.nhtsa.dot.gov/staticfiles/DOT/NHTSA/Vehicle%20Safety/Test%20Procedures/Associated%20Files/TP120-03.pdf Laboratory Test Procedure for FMVSS 120
  4. http://www.canlii.org/en/ca/laws/regu/sor-95-148/latest/sor-95-148.html Motor Vehicle Tire Safety Regulations SOR 95-148
  5. Web site: ISO - 83.160.10 - Road vehicle tyres. 2021-05-20. www.iso.org.
  6. Web site: Malinverni . Pier Giovanni . More than 50 years of standardisation . The European Tyre and Rim Technical Organisation.
  7. http://www.drtheo.nl/CX/TRX-history.htm A brief history of radial tires and the offbeat TRX system
  8. Similarly, whilst most bicycle wheels have a diameter measured in inches, the 700mm wheel (=27.56") is increasingly common.
  9. Web site: All Tire Pressures, Models, Tire Types and more . 2024-11-11 . tirepressure.org.
  10. Web site: Load Index Chart . 2025-02-05 . www.tyreteam.co.nz.
  11. Web site: What is Tire Load Index? View Tire Load Index Chart Wheel Works . 2025-02-05 . www.wheelworks.net.
  12. Web site: Tire Load Index . 2025-02-05 . Chaoyang Tires, LLC . en-US.
  13. Web site: Tyres . Watling . 2019-04-01 . Understanding the Tyre Load Index Β» Watling Tyres Autocentre . 2025-02-05 . Watling Tyres Autocentre . en-GB.
  14. Web site: Load Speed Index of OTR Tires: Capacity & Speed Guide . 2025-02-05 . Magna Tyres . en.
  15. Web site: Council Directive 92/23/EEC of 31 March 1992 relating to tyres for motor vehicles and their trailers and to their fitting . 2014-12-06 . THE COUNCIL OF THE EUROPEAN COMMUNITIES.
  16. Web site: How to calculate speed ratings . September 16, 2014 . 2014-12-06 . Auto Motor Γ–l.
  17. Web site: Goodyear Tires . What is the Tire Date Code? . goodyear.com . 2 January 2026 . https://web.archive.org/web/20230502184712/https://www.goodyear.com/en_US/learn/tire-basics/tire-date-code.html . 2 May 2023 . Tire Identification Number (TIN)...Because these characters are optional for the manufacturer, the TIN can be any length up to a maximum of twelve characters. The final four digits, for any tire made since the year 2000, are the tire date code and represent the date of manufacture. The first two of these digits designates the week of the year the tires were made, and the final two digits are the last two digits of the year of manufacture. (For example, 1319 means the thirteenth week of 2019.) ... If your tires were made before the year 2000, the date code will be only 3 digits – the first two digits again listing the week of the year, and the last digit being the last digit of the year of the tire’s manufacture. This means a date code of β€œ529” could mean the tire was manufactured in December 1999, or December 1989 – or even December 1979..
  18. Web site: Goodyear Tire Recall - Goodyear Tires . www.goodyear.com.
  19. https://www.law.cornell.edu/cfr/text/49/574.5 "49 CFR 574.5 - Tire identification requirements."
  20. Web site: Dept. of Transportation issues new DOT codes . March 8, 2016 .
  21. Web site: Complete List of Tire DOT Codes by Manufacturer . www.wfirm.com. January 11, 2021 .
  22. Web site: UN ECE . AGREEMENT CONCERNING THE ADOPTION OF UNIFORM TECHNICAL PRESCRIPTIONS FOR WHEELED VEHICLES, EQUIPMENT AND PARTS WHICH CAN BE FITTED AND/OR BE USED ON WHEELED VEHICLES AND THE CONDITIONS FOR RECIPROCAL RECOGNITION OF APPROVALS GRANTED ON THE BASIS OF THESE PRESCRIPTIONS Addendum 6: Regulation No. 7 Revision 5 . unece.org . 2 January 2026 . https://web.archive.org/web/20240616125402/https://unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/r7rev5e.pdf . 16 June 2024 . 4.2.1. An international approval mark, comprising: 4.2.1.1. A circle surrounding the letter "E" followed by the distinguishing number of the country which has granted approval;.
  23. Web site: ATIC: Australian Tyre Industry Council, Ltd. . What are E (or e) markings on a tyre . 2 January 2026 . https://web.archive.org/web/20220130123429/https://static1.squarespace.com/static/6052f822e4173f257d77b9e8/t/60c6de17a39fa145da494c0d/1623645720830/14+What+are+E+markings+on+a+Tyre.pdf . 30 January 2022.
  24. Web site: HTQS . Guide to E-Mark Certification . https://web.archive.org/web/20210318104516/https://www.hqts.com/e-mark-certification/ . 18 March 2021 . The first set of regulations was initially developed through the European Commission (EC) to create a common set of vehicle regulations for all EU member states. Approval is shown with the lower-case β€œe”. The second set of parallel vehicle regulations have been created through the United Nations Economic Commission for Europe (ECE). While the UN regulations cover nearly identical requirements, they are more globally applicable rather than simply being in place for the EU. Products certified to the UNECE regulations are marked with an upper-case β€œE”. Over the past several years the European Commission has simplified vehicle approvals by acceding its own community-wide regulations to those of the UNECE. Now only a single ECE type approval for vehicles and vehicle ESAs is required for all of Europe. This single type approval is denoted by having the upper-case β€œE”-mark placed on the vehicle or ESA..
  25. Book: Jazar, Reza N. . Vehicle Dynamics: Theory and Application . 2013-11-19 . Springer Science & Business Media . 9781461485445 . en.
  26. Web site: FAQ's. 2013-06-27.
  27. "2010 Year Book", The Tire and Rim Association, Inc., Preface p XVII
  28. "Bridgestone Product Reference Guide", The Bridgestone Tire & Rubber Co.
  29. "Bridgestone Product Reference Guide", The Bridgestone Tire & Rubber Co., Core Tire Knowledge: Glossary
  30. Web site: Sullivan Tire and Auto Service . What Do the Numbers and Letters on Your Tire's Sidewall Mean? . sullivantire.com . https://web.archive.org/web/20251007094342/https://www.sullivantire.com/blog/tires/what-do-the-numbers-and-letters-on-your-tires-sidewall-mean . live . 7 October 2025 . 11 January 2022 . Winter tires may also have added an "E" to the code to indicate extreme winter weather. It can be seen listed as "M+SE"..
  31. Web site: MERCEDES-BENZ ORIGINAL EXTENDED TIRES . Tire Rack .
  32. Web site: Tire care – Match mounting . Yokohama Tire Corporation .
  33. "2010 Year Book", The Tire and Rim Association, Inc.
  34. Web site: Vintage Tire Size Conversion Chart .
  35. Web site: Tire Size Conversion Chart .

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Tire code".

Except where otherwise indicated, Everything.Explained.Today is © Copyright 2009-2026, A B Cryer, All Rights Reserved. Cookie policy.