Every tire sold in the United States has a standardized size code molded into its sidewall, and understanding it is the first step to making a smart purchase. A typical size looks something like P225/65R17 102T. While that string of characters might seem like gibberish, each segment tells you something specific about the tire's dimensions, construction, and capabilities. Once you break it down, reading tire sizes becomes second nature.
The first letter indicates the tire's intended vehicle class. "P" stands for P-Metric, meaning it's designed for passenger vehicles like cars, SUVs, and light trucks. "LT" stands for Light Truck and signals a heavier-duty construction for pickups and commercial vans. If there's no letter at all, the tire follows the European metric standard, which is functionally similar to P-Metric for most drivers. Next comes the three-digit number — in our example, 225 — which is the section width of the tire in millimeters measured from sidewall to sidewall when properly mounted and inflated.
After the slash, the two-digit number (65 in our example) is the aspect ratio, which expresses the sidewall height as a percentage of the section width. A lower aspect ratio means a shorter, stiffer sidewall and typically sportier handling, while a higher number means a taller sidewall and a more cushioned ride. The letter "R" indicates radial construction, which is the standard for virtually all modern tires. The two-digit number that follows (17) is the wheel diameter in inches that the tire is designed to fit.
The final group — 102T in our example — is the service description. The number (102) is the load index, which tells you the maximum weight each tire can support when properly inflated. You can look up load index charts to find the exact weight in pounds. The letter (T) is the speed rating, indicating the maximum sustained speed the tire is engineered to handle safely. Common speed ratings include S (112 mph), T (118 mph), H (130 mph), V (149 mph), W (168 mph), and Y (186 mph). Always replace your tires with the same size and equal or higher load and speed ratings recommended by your vehicle manufacturer.
Armed with this knowledge, you can now decode any tire sidewall in seconds. When shopping at Ship.Tires, simply enter your tire size or use our vehicle lookup tool to find the exact match for your car, truck, or SUV. If you're ever unsure, our support team is happy to double-check your fitment before you place your order.