Sizing
Every tire sold in the United States contains codes to reveal the general build and expected use of the tire. In the United States, Canada, and Mexico, most tires utilize the “p-metric” sizing guide. If a tire has a size of P235/55R15, the “P” means a passenger tire. If a tire has a size of LT265/65R16, the “LT” means a Light Truck tire. The next set of numbers, in the example above “235”, reveals the tire’s section width in millimeters from sidewall to sidewall. In the example above, the “55” reveals the tire’s aspect ratio, the height of the sidewall expressed in the percent of the tire section width. The “R” in the above example stands for “Radial”. The final number in the sizing code contains the width of the rim used to mount the tire.
Load Index
The sidewall of every tire sold in the United States contains a load index, which reveals the maximum load a tire can carry at the speed indicated on the tire’s sidewall. Most commonly, a “SL” tells the consumer that the tire possesses a standard load. A p205/65R15 standard-load tire inflated to 26 PSI (pounds per square inch) can safely carry a load of 1213 pounds. With a PSI of 32, the tire can carry a load of 1334 pounds. A tire with a PSI of 38 can safely carry a load of 1400 pounds. Sometimes, a tire with a larger rim can carry less a load. A p205/60R16, inflated with 26 PSI, can carry a load of 1069 pounds. The same tire, inflated to 32 PSI, can safely carry a load of 1257. Finally, the same tire inflated to 38 PSI, can carry a load of 1389 pounds.
Speed Rating
Every tire sold in the United States reveals the speed rating on its sidewall, which tells the consumer the maximum speed a given tire can operate under a given load index. The Speed symbol is a letter, from L-Y. A tire with an “L” speed symbol can safely operate at 75 mph. This speed rating is rare. More typically, a tire sold in the United States will possess a speed rating of “P” or “Q”, which means the tire can safely operate under standard load conditions at 93 miles per hour (for “P”) and 99 miles per hour (for “Q”).
DOT Code
Every tire sold in the United States is required to meet the standards set up by the United States Department of Transportation. When these standards are satisfied through testing, the tire receives a DOT Code. The code typically has 12 characters. An example DOT code could be DOT AB C8 VXYZ 0110. “DOT” means the tire has met the Department of Transportation standards. The next few characters tell the consumer the manufacturer of the tire and the plant ID of the tire plant that manufactured the tire. The next few symbols, VXYZ in the example above, reveals the manufacturer’s code for the specific tire manufactured. Finally, and perhaps most important to the consumer, is the date code. These four numbers tell the consumer the week and year the tire was manufactured. Particular note should be made of this code at purchase, as no one wants to buy a “new tire” that was manufactured a year before purchase. Tires age, regardless of use.
Watts Guerra LLP has been prosecuting defective tire cases for two decades. We’ve seen all types of failure. But, consumers can help themselves by understanding the limits to a tire, both in regards to speed and load. Never operate a tire in a fashion that is not contemplated by the tire manufacturer. However, under normal operation, tires occasionally fail, causing catastrophic damage. Watts Guerra LLP can help identify the cause of the failure and pursue a remedy against the tire manufacturer.
Written by:
Guy L. Watts, II
Watts Guerra LLP
4 Dominion Drive, Bldg 3, Suite 100
San Antonio, Texas 78257
Phone (210) 447-0500
© Watts Guerra LLP 2015
