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Tire Labeling
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What information can be found on the sidewall of a tire?
Tire Size. The tire size printed on both sidewalls is a combination of values that define the size, construction, load carrying capacity, speed rating of a tire, and the type of vehicle on which the tire can be used. The first designation is the vehicle type—“P” for passenger rated tires, “LT” for light truck rated tires, or “ST” for trailer rated tires. The next value is the tire width in millimeters at the cross-section (the widest point in the sidewall). The value that follows the forward slash is the aspect ratio. This number is a ratio of the width to the height of the tire. The next value in the sequence is the type of ply construction in the tire—“R” is the most common construction used on passenger vehicles and light trucks and it designates radial ply construction. Some tires will show a “D” designation for diagonal ply, also called bias ply or cross ply. The next value is the rim diameter specified in inches. The load index follows the rim diameter. This number is used to compare the carrying capacities of various tire sizes. The final value in the tire size sequence is the tire speed rating as approved by the tire manufacturer. Examples of passenger and light truck tire sizes are P225/60R16 97H and LT235/85R16 116R. Note that the load range/speed rating may be omitted on older designs. In such cases the load range will be on the tire sidewall but not as part of the size.
Maximum Inflation Pressure and Maximum Carrying Capacity. These values are in very small print near the edge of the rim. Maximum carrying capacities are expressed in both pounds (LBS) and kilograms (KG). Maximum air pressures are shown in both pounds per square inch (PSI) and kilopascals (KPA). Note that these values are the maximum carrying capacity at the maximum inflation pressure for a tire and not the recommended pressure levels. The recommended inflation level is specified for the recommended tire size by the vehicle manufacturer and noted on the vehicle placard.
Manufacturer DOT Label. This is an identification number mandated by the U. S. Department of Transportation (DOT). The required number, sometimes mistakenly called a serial number, is located adjacent to the rim edge. The “DOT” designation will be next to the coded information. The first two alpha-numeric characters represent the manufacturer and the facility in which the tire was made. The next two characters represent the size. The last three or four digits, depending on whether the tire was made before or after January 1,2000, are a code for the date of manufacture. The optional characters between the size code and the date code are for use by the manufacturer as they choose. This number will be important to identify a tire that is subject to a safety-related recall. Recently the DOT mandated that a partial DOT code be included on the opposite side of the tire to facilitate locating the full DOT code if it happened to be on the inboard sidewall.
Uniform Tire Quality Grade (UTQG) information. This rating system was mandated by the Department of Transportation in 1971 to aid consumers in comparing tires. The three rating indices are Tread wear, Traction, and Temperature. The DOT program requires that the manufacturer qualify the treadwear numbers by running an unspecified auto on a test track for a few thousand miles, extrapolating the results, and comparing the expected mileage against a non-existent control tire. While a very rough comparison could be made for comparative mileage expectancies within a tire brand, comparisons between brands are rather inaccurate. Traction ratings vary little among various brands and similar tread designs. The temperature ratings are meaningless. The whole system therefore yields little information that can be used for practical, real-life, comparisons by consumers.
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What is Tire Registration?
In 1971 the U. S. Department of Transportation mandated a system to recall tires suspected of being unsafe. The manufacturer is required to label tires by manufacturing location and date of manufacture. The manufacturer is also required to keep a list of purchasers and the tire identification codes on file in case a mandatory or voluntary tire recall is necessary. The retail tire dealer is required to furnish the purchaser of all highway-rated tires the forms needed to register their tires. Central Tire customarily registers the purchaser and the tire identification numbers so that the consumer does not have to do it.
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