How To Read A tire Sidewall

There is a lot of useful information molded into the sidewall of every tire. Included are manufacturer & tire name; section width; aspect ratio; construction; rim diameter; speed rating; load range; treadwear, temperature & traction labeling & other required designations.

SIZE
All tires sold in the United States must meet the size standards for bead shape, width, diameter & other parameters established by a recognized standardizing organization. World leaders among such organizations are the European Tire & Rim Technical Organization (ETRTO) & the U. S. Tire & Rim Association (T&RA). Both use a partially metric-based system. Virtually all passenger tires on the market today use the rim & tire sizing, load & inflation system established by these bodies. All U. S. highway tires must also meet U. S. D.O.T. standards as indicated by the letters 'D.O.T.' on the sidewall.

 

The several tire size designations in use today depend on when a vehicle was manufactured & whether it was domestically produced or imported. All tire-sizing systems used today provide information about a tire's dimensions. Among the most important for proper fitment is height, width & load carrying capacity.
P-Metric: This is the United States version of a metric sizing system established in 1976. P-Metric passenger car tire sizes begin with "P," which simply means "Passenger."

 

Metric: This European tire sizing system is similar to P-Metric but does not use the "P" designator.

 

Alphanumeric: This system was established in 1968 & is based on the tire's load carrying capacity, correlated to its overall size. The tire's capacity & size are indicated by letter designations from "A" (smallest tire, lowest capacity) to "N" (largest tire, highest capacity). An example of an Alphanumeric tire size is BR78-13. "B" shows size/load, "R" indicates radial construction, "78" is the aspect ratio, & "13" is the wheel size in inches.

 

Numeric: This is the oldest standardized tire sizing system for passenger car tires. When this system was adopted, tire aspect ratios were either 92 or 82. For example, a 7.00-14 tire has a section width of 7 inches, a rim diameter of 14 inches & an aspect ratio of 92. The low profile equivalent size tire with an aspect ratio of 82 would be 7.35-14.

Example: P215/65R15 89H

P PASSENGER (P-METRIC/NON-P-METRIC)
This indicates a passenger car tire. If the first character in the size designation is a "P," the tire is a "P-Metric" tire & is engineered to standards set by the T&RA. If there is no "P", the tire is engineered to ETRTO standards & is a metric tire. The standards set by T&RA & ETRTO have evolved together & are virtually interchangeable.

 

215 SECTION WIDTH
These numerals indicate the tire section width in millimeters. This is the dimension from sidewall to sidewall. A tire's section width will vary depending on the rim to which it is fitted. The section width will be larger on a wide rim & smaller on a narrow rim. Therefore, each tire is measured to specific rim width. (To convert millimeters into inches, divide by 25.4.)

 

65 ASPECT RATIO
This two-digit number indicates the tire's aspect ratio. It compares the tire's inflated section height, which is the distance from the bead to the tread, to its section width (maximum). An aspect ratio of 65 means that the tire's section height is 65% of the tire's section width. For clarity, the section width in millimeters is separated from the aspect ratio by a slash (/).

 

R CONSTRUCTION
This letter indicates the type of ply construction in the tire's casing or carcass. "R" means radial. "D" means diagonal, referring to bias ply tires. "B" means belted for belted-bias ply tires. Never mix radial tires with any other construction on a car.

 

15 RIM DIAMETER
The "15" indicates the rim diameter in inches. It is the diameter of the tire bead seat ledge in the rim. Most tires are built to inch standards for rim diameters. However, some tires are built to millimetric rim dimensions. Always match the tire's rim diameter to the wheel rim diameter. This is important for safety.
NOTE: A millimetric rim has a different shape than an inch rim; they are not interchangeable.

 

89H SERVICE DESCRIPTION
The service description is an alphanumeric combination, consisting of two parts, a number & a letter. In this example, "89" is the load index, which represents the load carrying capacity. (All passenger car tires in the U.S. are also marked with their actual load limit in pounds.) The letter part is the speed symbol, 'H,' in this example. This is the maximum speed for which the tire is rated at the load specified by the load index. In this example, 'H' means speeds up to 130 mph. Dunlop does not recommend the use of any of its products in excess of legal speed limits. Speed Ratings do not necessarily imply that the performance (handling & grip) of the tire meet the performance standards implied by the ratings.

 

Tire speed ratings must exceed the maximum speed capability of the vehicle to which they are fitted. Not all tires sold in the U.S. are speed rated, although many modern performance & luxury cars are equipped with speed rated Original Equipment tires. It is important to remember this when replacing the tires on your vehicle. Replace tires with equivalent or higher speed rated tires. Do not downgrade speed ratings from Original Equipment ratings.

 

NOTE: Speed Ratings - where applied are indicative of high performance characteristics based on European ECE 30 Indoor Wheel testing as performed by Dunlop & are not valid for damaged, altered, repaired, under-inflated, overloaded, excessively worn, or re-treaded tires. Dunlop does not recommend the use of any of its products in excess of legal speed limits.

 

SERVICE INDICATORS
Some tires carry additional markings related to service. An M&S or M+S designation means the tire is rated suitable by the manufacturer for mud & snow use. The guidelines are set by the Rubber Manufacturers Association (RMA) in the United States.

 

ALL-SEASON DESIGNATION
This is a marking which means that the tire meets M&S/M+S requirements without the drawbacks of noise & rolling resistance associated with the traditional deep-lug winter tires. The M&S/M+S designation means that the tire is suitable for normal all-weather driving applications. Tires that meet the requirements of the M& S designation have better winter traction compared to those without the M&S symbol.

 

North American tire manufacturers & the RMA have established a voluntary, industry-wide definition for passenger & light truck tires intended for use in SEVERE SNOW CONDITIONS. Tires must meet a performance-based criteria featuring tread pattern, construction elements & materials which generally provide snow performance superior to that of tires bearing the RMA current M&S Rating. Such tires will display a mountain/snowflake symbol.

 

D.O.T.
The 10 digit D.O.T. code number molded into the sidewall designates the manufacturer & plant where the tire was produced, the tire line & size, & the week & year the tire was manufactured.

 

MAXIMUM PRESSURE/LOAD
All passenger tires are marked on the sidewalls to indicate maximum load capacity & maximum inflation pressure. Truck tires will indicate recommended pressure for maximum loads for both dual & single application.

 

HARMONIC MARKINGS
Red dots on Dunlop high performance tires for match mounting purposes. These dots mark the 'high spot' of the tire, which is then matched with the 'low spot' on the rim to cancel out harmonic vibration.

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