Did you ever wonder what all the letters and numbers mean on the sidewall of your car tires?
There is a more useful information on your tires than you realize. Aside from the brand, model and size of the tire there are also U.S. Department of Transportation (DOT) and safety standard markings. These indicate that the tire meets the safety requirements as determined by the DOT. Near these markings, there is also the Uniform Tire Quality Grading (UTQG) code as well as load, speed and maximum inflation pressure specifications, just to name a few. Let’s take a closer look.
1‑4) Tire Size Information.
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).
- The number after the slash indicates its aspect ratio, or profile. This tire's sidewall height is 40 percent of its width.
- The "R" stands for radial construction (rarer bias-ply and belted tires are denoted by a D and B, respectively).
- 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) Tire Service Description
This alphanumeric code 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.
- L - 75 mph (120.7 kmph)
- M - 81 mph (130.36 kmph)
- N - 87 mph (140.01 kmph)
- P - 93 mph (149.67 kmph)
- Q - 99 mph (159.33 kmph)
- R - 106 mph (170.59kmph)
- S - 112 mph (180.25 kmph)
- T - 118 mph (189.90 kmph)
- U - 124 mph (199.56 kmph)
- H - 130 mph (209.21 kmph)
- V - 149 mph (239.79 kmph)
- W - 168 mph (270.37 kmph)
- Y - 186 mph (299.34 kmph)
- (Y) - more than 186 mph (more than 300 kmph)
6) The red dot on your car's tire. What does it mean?
Many but not all tire manufacturers 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.
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.
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) M+S Mud and Snow
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) OE Original Equipment
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) Tire Materials
This is a list of the tire's construction materials, of interest primarily to tire engineers and tire geeks.
14) DOT Labeling
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.