All those numbers on a tire’s sidewall might seem like gibberish, but each one tells you something about the tire. Here’s how to decipher them.
Car tires are a great example of something vitally important, but that most of us forget about aside from the rare occasions we have to replace them. That’s probably a testament to how great modern cars and tires have gotten, but it also means that when the time comes to read the side of a tire, we don’t really know what we’re looking at.
That’s a problem because all of those numbers mean something and every one of them tells you something about your tire and its capabilities. Some are more obvious; some are pretty obscure. But fear not, because you don’t need to be a qualified mechanic to know what all of those numbers mean.
The Important Details
Some information printed on tires is more important, at least when it comes to shopping for new ones. First, let’s take a look at a fairly standard set of numbers—something like P225/50/R17 98H.
- The “P” at the beginning of this number means that the tire is meant for a passenger vehicle. If it had an “LT” then it would be a tire designed for a Light Truck—if there’s no letter, then the tire likely originated from Europe and is similar to one with a “P” designation.
- The “225” that comes next is the width of the tire. It’s a measurement in millimeters from the inner to the outer sidewall. This measurement is taken for specific rim widths, so the actual width of the tire depends on the rim on which it’s mounted.
- The “50” is the aspect ratio of the tire, which is the tire’s height in relation to its width. In our example here, the tire is 50% as tall as it is wide.
- The “R17” in our example signifies that tire is of radial construction, and that it is 17 inches in diameter. Instead of an “R,” you might also see a “B” (which stands for belted bias) or “D” (which stands for diagonal bias). You don’t need to worry too much about those—the numbers are what makes sure the tire will fit.
- The final “98H” in our example indicates the load index and speed rating of the tire. The load index informs you how much weight a tire can support once it is correctly inflated, and it ranges from 75 to 105 for most passenger tires. The speed rating letter corresponds to one of many different maximum speeds.
- Q: 100 MPH
- S: 112 MPH
- T: 118 MPH
- U: 124 MPH
- H: 130 MPH
- V: 149 MPH
- W: 168 MPH
- Y: 186 MPH]
- Z: Over 149 MPH
Uniform Tire Quality Rating
Tires also have other numbers that, while important in their own regard, are probably not something you need to worry about when shopping for a new tire.
These numbers make up the Uniform Tire Quality Grading (or UTQG) and are provided by the U.S. Department of Transportation (USDOT). The UTQG is made up of three ratings:
- Treadwear: Treadware grades are comparative and based on actual road testing against a known test tire. A grade of 100 means that the tire would last the same length as the test tire. A 200 rating means it would last twice as long, 300 three times as long, and so on.
- Temperature Resistance: Temperature Grades are offered with an A grade meaning your tire is going to be fine at dissipating heat at speeds of over 115mph. A B grade is good for 100-115mph, while a C grade will suffice for speeds up to 100mph.
- Traction: Traction Grades come in ratings of AA, A, B, and C and are in order of their ability to provide traction in wet conditions. AA is an outstanding rating. C, not so much.
Buying car tires needn’t be a confusing endeavor and armed with this information, you’ll be able to make a good, informed decision about the tires that are on your car’s wheels the next time you need to replace them.