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Understanding Tire Talk
If you're confused by all those numbers and letters printed on tires, you're not alone.
  Typically on a tire's sidewall, you'll find the model or name of the tire and opposite that, the manufacturer. On the space between the model and manufacturer, you'll find something like "LT 245/75R16 90H" on one side and something like "TRACTION A TREADWEAR 220 TEMPERATURE B" on the other. In smaller type near the bead, you'll find information on maximum cold inflation and load limits, tire ply composition and materials used, and even the U.S. Department of Transportation safety standard codes relating to that particular tire.
  Okay. But what does it all mean? This diagram from Cooper Tire Company should help.
  If we break down the coding on a pickup tire, this is what it says:
  LT - This is the type of tire. LT means light truck. You'll find these on pickups and some SUVs. P means passenger car.
  275 - Width of the tire, in millimeters.
  75 - Designates the aspect ratio, or ratio of height to width so 75 means the tire is 75 percent as tall as it is wide.
  R - Designates radial construction. For a bias tire, you might find D, for diagonal, or B for belted bias.
  17 - Indicates the nominal wheel dimension to fit the tire, in inches. The wheel diameter on the vehicle and this number on the tire must always match.
  95H - These are load and speed ratings for the tire. Such information is not required on the tire, so don't panic if it's not there. But if you're concerned about your tires' performance under load or at certain speeds, you should probably look for this information or ask your dealer before you buy the tires. The number relates to load. The higher the number, the greater the load carrying capacity of the tire. The letter is the speed rating, based on indoor wheel tests and doesn't represent a safe or acceptable driving speed.
  Other information that might be important is treadwear, traction and temperature, which appear opposite the size and load ratings.
  The treadwear number compares the tire against a government-mandated standard that is equal to 100. A treadwear rating of 220 means the tread should last 2.2 times as long as the federally imposed standard.
  The traction scale is from C to AA, meaning that a tire with a C rating has the lowest level of road grip and an AA traction tire has the most.
  The temperature rating indicates the tire's ability to disperse heat. This may not be important on tires that run at low speed on soft surfaces, but it is something to look for on tires that will see high speeds on hard surfaces under load. The rating scale is C to A, with an A rated tire being best able to resist heat buildup.

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2003 - Volume #27, Issue #1