How to Read Tire Sizes

What Does All This Mean?

A first glance of an untrained eye at a tire can be confusing. Furthermore, until you learn what each indicator means, shopping for tires on a rack in a box store can be very frustrating. If you bring your vehicle to O’Berry’s Service Center in Emporia, Virginia, however, you won’t have to worry at all. Since 1991, we’ve been helping the motoring public avoid the stress, confusion, and frustration of purchasing and maintaining tires.

A Reading Lesson

We get it. If you’re not yet familiar with tire markings, you may perceive the writing on the sidewall to be a jumble of letters and numbers that might as well be written in Hieroglyphics. We’d like to offer a quick lesson in reading sidewalls. Not only will you feel more comfortable understanding what’s printed on your tires, but you’ll also be able to glean important and valuable information whenever you need it. First, things are abbreviated. There’s too much to fit into a small space to spell everything out in long form. The US Department of Transportation (DOT) requires that certain facts related to safety standards be provided on each tire. One such piece of information is the tire class. It’s indicated by the first letter. For example, “P” indicates intended use on passenger cars while “LT” stands for light trucks on all US tires. (Note: European metric tires omit this initial letter.) The tread width (expressed in millimeters or mm) is provided using the 3 digits following the letter of the tire class. Tread width is measured from one sidewall to the other, so a 225 marking relates to buyers that the tread is 225mm wide. The next digits are followed by an R. Known as the aspect ratio and given as a percentage, these express the relationship between the tread width and sidewall height. The sidewall height of a 45 R tire, for instance, is 45% of the tread width. The next letter (A through Z) provides the tire’s speed rating. That’s the maximum safe operating speed of the tire when it’s in excellent condition. Corresponding tables reference the speed range for each letter with “Z” being the highest. “Z” range tires also give more accurate maximum safe speeds using “W” and “Y” ranges, too. Radial tires will then display an “R.” Radials are constructed using multiple layers of cords. The subsequent two digits provide the diameter. For example, 20 indicates that the tire has a 20 inch diameter. The load index, a measure of how much a tire can safely hold under operating conditions, is the following multiple-digit expression. Last, you notice the operational speed rating. The DOT also mandates that manufacturers provide plant location and production date, so you’ll notice abbreviations for those, too. In addition to tire size, the tread pattern type may be provided, as well. The Uniform Tire Quality Grading (UTQG) marking shares information about the durability and weather uses. The PSI gives the maximum inflation (expressed as pounds per square inch).

All the Help You Need for Tires

If you’re still feeling some angst, aren’t equipped to change your own tires, or simply prefer not to deal with it, let us help. The certified technicians at O’Berry’s Service Center are happy to take care of all your tire needs–whether you need purchase, maintenance, or repair.

Written by Developer Autoshop