How to Read Tire Size Numbers: Complete Guide
Every tire sold in the United States has a standardized size code printed on its sidewall. Understanding this code is essential for buying the right replacement tires. A typical tire size looks like this: P225/65R17 102H. Each part tells you something specific about the tire's dimensions and capabilities.
Breaking Down the Code
P stands for Passenger, meaning the tire is designed for passenger vehicles. You may also see LT (Light Truck) on trucks and SUVs, or no letter at all on Euro-metric tires.
225 is the tire width in millimeters, measured from sidewall to sidewall. Wider tires generally provide more grip, while narrower tires reduce rolling resistance for better fuel economy.
65 is the aspect ratio, expressed as a percentage. This means the sidewall height is 65% of the tire width. Lower numbers (like 35 or 40) indicate a shorter sidewall, which improves handling response but gives a firmer ride. Higher numbers (65, 70, 75) mean a taller sidewall for more comfort.
R stands for Radial construction, which is the standard for modern tires. Nearly all passenger tires today are radial.
17 is the rim diameter in inches. This must match your wheel size exactly.
Load Index and Speed Rating
102 is the load index, indicating the maximum weight each tire can support. A load index of 102 means 1,874 pounds per tire. Higher numbers support more weight, which matters for trucks and SUVs that carry heavy loads.
H is the speed rating, indicating the maximum sustained speed the tire is designed for. H means 130 mph. Common ratings include S (112 mph), T (118 mph), H (130 mph), V (149 mph), W (168 mph), and Y (186 mph).
Additional Markings
Look for M+S (Mud and Snow) indicating all-season capability, or the three-peak mountain snowflake symbol for tires tested in severe winter conditions. The UTQG (Uniform Tire Quality Grading) ratings cover treadwear, traction, and temperature resistance.
Recommended Tools for Tire Maintenance
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