How to read a tire code
Have you ever been curious about those letters and numbers on the sidewall or how to read tire code? They contain much more information than you think. Not only can you identify the brand, size, and model of the tire, you can also find other important safety information like maximum tire pressure, load index and speed rating. In addition, there are Uniform Tire Quality Grading (UTQG) codes as well, see this article for more. Here are the tire code definitions:
VEHICLE CLASS – P215/65R15 89H
P: Passenger Car
LT: Light Truck
SP: Special Trailer
T: Temporary (restricted usage for ‘Space-Saver’ spare wheels)
3 DIGIT NUMBER – P215/65R15 89H
The ‘nominal section width’ of the tire in millimeteres; the widest point from both outer edges.
2 OR 3 DIGIT NUMBER – P215/65R15 89H
The ‘aspect ratio’ of the sidewall height to the total width of the tire, as a percentage. If no information is provided, 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 – P215/65R15 89H
Indicating construction of the fabric carcass of the tire.
B: bias belt
2 DIGIT NUMBER – P215/65R15 89H
The wheel diameter, in inches, that the tire will fit.
2 OR 3 DIGIT NUMBER – P215/65R15 89H
Load index; see below.
1 OR 2 DIGIT/LETTER COMBO – P215/65R15 89H
speed rating; see below.
- A 2
- B 4
- C 6
- D 8
- E 10
- F 12
- G 14
- H 16
- J 18
- L 20
- M 22
- N 24
Please note that there is no correlation 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 or 55 PSI, Load Range D tires may require 50 PSI or 65 PSI, and Load Range E tires may require 65 PSI or 80 PSI to achieve their Load Index and Maximum Loads. This is also the case in the tables published by major tire manufacturers, who follow TRA standards and have multiple inflation pressures for the same Load Range in the tires they sell.
It is essential to consult the guides such as those mentioned above 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.
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 while P-Metric standards measure the load capacity at an inflation pressure of 35 PSI. 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 (in pounds), 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 pounds at 35 PSI. A P215/50R13 with the same load index of 84 only has a load rating of 1091 pounds, also at 35 PSI.
The speed rating code is made up of either one or two letters, or one letter and one number. It indicates the maximum permitted speed that the tire can sustain for a 10 minute endurance without being in danger.Tires with a speed rating higher than 186 mph (300 km/h) include 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). If a tire is replaced with a lower speed rating than originally specified by the vehicle manufacturer, this may render the vehicle insurance invalid.
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. 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.
There are numerous other markings on a typical tire, these may include:
- M+S, or M&S: Mud and Snow; all-weather tires, with above-average traction in muddy or very light snowy conditions, and for low ambient temperatures. Not classified as a winter tire unless it has the snowflake and mountain symbol. Studded tires have an additional letter, ‘E’ (M+SE).
- BSW: Black Sidewall
- WSW: White Sidewall
- OWL: Outline White Lettering
- VSB: Vertical Serrated Band
- 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 Transportation (DOT). It specifies the company, factory, mold, batch, and date of production (2 digits for week of the year plus 2 digits for year; or 2 digits for week of the year plus 1 digit for year for tires made prior to 2000).
- 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 other small indicator, 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; tire for vehicles of heavier standard weights
- RF: Reinforced tires
- 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.
- M0: Original tires for Mercedes-Benz
- N*: Original tires for Porsche
- ‘Star’: Original tires for BMW