The sidewall of your tire contains a wealth of information—if you know how to decode it. Understanding these markings helps you purchase the right replacement, check tire age, and ensure proper inflation. The code may appear cryptic at first, but each character tells a specific story about your tire’s capabilities and origins.
The Tire Size Code
The most prominent sequence on the sidewall is the tire size, formatted like “P 205/55 R 16 91 V.” The first letter, P, indicates the tire is designed for passenger vehicles. Other letters include LT for light trucks and no letter for European metric sizes.
The three-digit number, 205, represents the tire’s width in millimeters from sidewall to sidewall. Wider tires provide more grip but may affect fuel economy. The two-digit number following the slash, 55, is the aspect ratio—the sidewall height expressed as a percentage of the width. A lower number means shorter sidewalls, which typically improve handling but deliver a firmer ride.
The letter R stands for radial construction, the standard for modern tires. The following two-digit number, 16, indicates the wheel diameter in inches that the tire fits. The two-digit number after that, 91, is the load index—a numerical code corresponding to the maximum weight the tire can carry. Finally, the letter V is the speed rating, indicating the maximum safe speed the tire can sustain.
Production Date
The DOT code, required by the U.S. Department of Transportation, ends with a four-digit number that reveals when the tire was manufactured. The first two digits represent the week, and the last two indicate the year. For example, “3523” means the tire was produced in the 35th week of 2023. This date matters because tires degrade over time, regardless of tread depth. Most manufacturers recommend replacement after six years, and no tire should remain in service beyond ten years. Always check this date when purchasing new tires.
Load Index and Speed Rating
The load index is a numerical code from 71 to 110, corresponding to specific weight capacities. A load index of 91, for example, equates to 615 kilograms per tire. Consult a load index chart to understand the exact capacity. The speed rating, expressed as a letter, indicates the maximum speed the tire can safely sustain. Common ratings include S (180 km/h), H (210 km/h), V (240 km/h), and W (270 km/h).
Treadwear, Traction, and Temperature
The UTQG (Uniform Tire Quality Grading) system provides three key ratings. Treadwear is a number comparing expected wear against a government standard. A tire graded 400 is theoretically expected to last twice as long as a tire graded 200, though comparisons across manufacturers are not always precise. Traction is graded AA, A, B, or C, measuring wet stopping ability on asphalt and concrete. Temperature is graded A, B, or C, indicating resistance to heat generation at speed. A temperature grade of A offers the greatest safety margin at highway speeds.
M+S and 3PMSF
Many tires carry an M+S (Mud and Snow) marking, indicating they meet the manufacturer’s definition for moderate snow capability. However, this marking is self-certified and not rigorously standardized. The Three-Peak Mountain Snowflake (3PMSF) symbol indicates the tire has passed standardized tests for severe snow service and is the marking to look for on dedicated winter tires.
Other Markings
Additional markings include the maximum inflation pressure, expressed in PSI or kPa, and the TWI (Tread Wear Indicator) markers that show where to find built-in wear bars within the tread grooves.
Understanding these markings takes minutes but pays dividends throughout your tire ownership experience. Read your tire sidewall with confidence, knowing exactly what each character means and how it affects your driving.
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