Let us help you decode the tire size, age, speed rating, and other important data that can be found on the sidewall.
Want to know how old your tires are or what size your tires are? You need to know how to read tire sidewall information, the alphanumeric code stamped on to the side of your tires. But if you've ever looked at the sidewall of a tire and thought that the blizzard of numbers, letters, and words was as confusing as hieroglyphics, we understand. The alphabet soup on tires' sidewalls can be off-putting, but it's pretty easy once you know what you're looking at. 19 In Wheels 5x114 3
Beyond the brand (Michelin, Continental, Hankook, etc.) and model names of the tire, the plethora of data stamped on the sidewall is there largely to satisfy government regulations, which require all manner of information—from when and where the tire was built to how durable it is. Not to worry. Let us be your Rosetta stone to deciphering the language of the tire sidewall. The numbers highlighted in pink on the sample tire below correspond to the explanations that follow.
1) These are some of the most important numbers on any tire, as they tell you how big your tires are. In this case, the tire is 245 millimeters at its widest point (when it's mounted on a wheel of a specified width).
2) The number after the slash indicates its aspect ratio, or profile. This tire's sidewall height is 40 percent of its width.
3) The "R" stands for radial construction (rarer bias-ply and belted tires are denoted by a D and B, respectively).
4) The number 18 indicates that this tire fits an 18-inch wheel. Sometimes, letters precede the first number. A "P" stands for p-metric, which is a tire used primarily on passenger cars. An "LT" indicates a light-truck tire. A "T" means it's a temporary spare. Some tires get a "Z" or an "F" attached to the radial indicator, denoting a Z-rated tire (see service description below) or a run-flat tire.
5) This alphanumeric code is the service description, which provides two key insights into the tire's performance: how much weight it can carry and how fast it can run safely—the latter another good indication of whether it's intended for a family sedan or a hot sporty machine. In our example, the "93" stands for the maximum-load rating of 1433 pounds. The letter W denotes the maximum speed rating, which translates 168 mph—not something intended for mom's minivan. See our list of speed ratings below, which range from a low of "L" (just 75 mph for some off-road tires) to a high of Y (186 mph). There is also one special ultrahigh speed rating: If a Y-rated tire has parentheses around its service description, say, "(93Y)," that means the tire is rated for speed "in excess of 186 mph." There are also Z-rated tires, but when that designation came out, no one thought a speed rating in excess of 149 mph would ever be needed. By definition, all W- and Y- rated tires are also Z-rated, though not all get a "Z" embossed on the sidewall.
6) Many but not all tiremakers note the heaviest spot of the tire with a red dot. It ultimately has no bearing on tire-and-wheel balance, so it's of little importance.
7) The numbers after the word "treadwear" indicate (surprise!) the treadwear of the tire, or how long it's likely to last. The higher the number, the more likely it is that you'll get more miles out of it. But the tests that determine tread life are not exact. The experts at tire-seller Tire Rack report that treadwear ratings can vary. They cite the example of two different tires they sell—one from Goodyear and the other from Continental—both of which offer an 80,000-mile tread-life warranty. You'd expect them to have similar, if not identical, treadwear ratings, but the Goodyear's is 740, while the Continental's is 600. So take this number as an indicator, but not an exact predictor, of how long a tire will last.
8‑9) The letter after the word "traction" is a rating that results from a test of how much grip a tire generates when dragged across wet pavement without the tire rotating. It's not of great relevance to today's cars, which have anti-lock brakes that keep the tires rolling even during emergency braking. The letter following the word "temperature" is an indicator of how well a tire dissipates heat, which increases severely at high speed. Again, it is of less importance than the tire's speed rating, which takes this into account.
10‑11) Some tires carry an "M+S" marking, which stands for "mud and snow." It means that the tire has some added capability in those circumstances because it has a little extra space between its tread blocks. But such tires are absolutely not winter (snow) tires and might not even be conventional all-season tires. That's where the three-peak mountain snowflake icon next to the M+S mark comes in. If a tire has that molded into its sidewall, it has significant snow capability and should be considered a viable winter tire.
12) This area of the tire may display what's called the original-equipment (OE) marking. Automakers sometimes take a standard, off-the-rack commodity tire and modify its construction or rubber compound to work better on one of their models. So, a Ford Escort and a Chevy Cruze might both be equipped with Firestone Firehawk AS tires that look virtually identical, but each car's tires might differ significantly in ways that affect the ride and handling. If your vehicle's tires carry an OE code, it's best to replace them with the same brand and model of tire wearing the same code—if you can. Tire stores and online retailers can help you with finding tires with the correct OE code for your vehicle.
13) This is a list of the tire's construction materials, of interest primarily to tire engineers and tire geeks.
14) Every tire sold in the U.S. must have U.S. Department of Transportation (DOT) labeling. The first two characters indicate the factory of manufacture, and the next five or six are manufacturer-specific jargon (for tracking purposes, as in the case of a recall). The last four numbers give the date of production which let you know how old your tires are with the first two digits indicating the week and the latter two the year (for example, "2318" means that tire was produced in the 23rd week of 2018). The European equivalent of the DOT code may also be present (it starts with an "e"), although fewer manufacturers are printing both on a tire's sidewall. If this string of numbers ends with "-S," it means the tire complies with European noise regulations.
Dave VanderWerp has spent more than 20 years in the automotive industry, in varied roles from engineering to product consulting, and now leading Car and Driver's vehicle-testing efforts. Dave got his very lucky start at C/D by happening to submit an unsolicited resume at just the right time to land a part-time road warrior job when he was a student at the University of Michigan, where he immediately became enthralled with the world of automotive journalism.
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