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Tire Numbers

Posted by: fullname Posted On: January 24th 2010 12:00:00 AM Sunday

What do all those numbers on a tire sidewall mean? The tire size is a combination of width, height, and wheel size. A common size designator is 225/60R16. The first number, 225 is the width of the tire from sidewall to sidewall in millimeters. The second number, 60 is known as the aspect ratio. It is the height of the sidewall expressed as a percentage of the width. The letter R denotes a steel-belted radial. The third number is the wheel size in inches. The service rating, printed after the size, is two numbers and a letter. The numbers are a load index. The number 87 is a common identifier and represents the tire's ability to safely carry 1,201 pounds. The higher the number, the more weight the tire is able to carry. The letter is a speed rating indicating the tires maximum safe speed. Most sedan tires are rated S and can be safely operated at 112 miles per hour. Performance tires for sports cars have a rating as high as V or Z and can be operated at speeds up to150 mph or greater. Next is the DOT number. It is a serial number required by the Federal Department of Transportation. It identifies the factory where the tire was manufactured and, more importantly, the last four digits indicate the week and year of manufacture. Tread wear, traction, and temperature numbers are results of government mandated tests known as Uniform Tire Quality Grade System.  They are indicators of the tire's performance parameters. A complete description of UTQGS ratings can be found at www.safercar.gov. These tests are performed by each manufacturer and are not meant for brand comparison.

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