15/05/2026
Technical Note: Deciphering Tire Sidewall Markings
The provided infographic breaks down the standardized alphanumeric code found on every tire sidewall. This code is essential for ensuring correct fitment, safety, and performance.
Breakdown of P 225 / 70 R 16 91 S
Vehicle Type (P): Stands for "Passenger." Other common prefixes include LT (Light Truck), ST (Special Trailer), or T (Temporary/Spare).
Width (225): The width of the tire in millimeters from sidewall to sidewall.
Aspect Ratio (70): This is the ratio of the height of the tire's cross-section to its width. A "70" means the height is 70% of the tire's width. Lower numbers indicate "low-profile" tires often seen on sports cars.
Construction (R): Stands for Radial, which is the industry standard where the internal ply cords run at 90 degrees to the direction of travel. You may occasionally see D (Diagonal/Bias ply) on older equipment.
Rim Diameter (16): The size of the wheel the tire is designed to fit, measured in inches.
Load Index (91): A numerical code that corresponds to the maximum weight the tire can support when properly inflated. In this case, "91" corresponds to 1,356 lbs (615 kg).
Speed Rating (S): A letter code indicating the maximum speed the tire can safely maintain over time. An "S" rating is certified for up to 112 mph (180 km/h).
Why These Specifications Matter
Safety & Load: Exceeding the Load Index can lead to heat-induced structural failure. Always ensure replacement tires meet or exceed the original equipment (OE) rating.
Speed Capability: High-performance vehicles require higher speed ratings (e.g., V, W, or Y) to handle the centrifugal forces and heat generated at high speeds.
Odometer Accuracy: Changing the Aspect Ratio or Rim Diameter without adjusting the other variables can change the overall rolling circumference, leading to inaccurate speedometer and odometer readings.
Maintenance Tip: When reading the sidewall, also look for the DOT code. The last four digits (e.g., 1226) indicate
