Tire Size Chart: Speed Ratings & Load Index

A tire sidewall encodes its dimensions, speed capability, and load capacity in a short alphanumeric string. Reading that code tells you what the tire can handle — and what to look for when comparing replacements or checking compatibility.

P-metric tire code decoder

A standard P-metric code such as P225/65R17 91H breaks down as follows:

Euro-metric tires (no P prefix, e.g. 225/65R17) use identical math and the same speed/load codes. The difference is load capacity — LT-metric tires have higher load ratings than the equivalent P-metric at the same inflation pressure.

Speed rating codes

Speed ratings define the maximum sustained speed a tire is designed to handle under load. Exceeding the rated speed is unsafe even if the tire appears undamaged.

Never downgrade the speed rating when replacing tires. A lower-rated tire on a vehicle originally equipped with a higher rating is unsafe and may void your insurance in some jurisdictions. Upgrading to a higher rating is generally acceptable.

Load index reference

The load index is a numerical code representing the maximum load capacity of a single tire. Total vehicle load capacity = load rating × 4 (for a four-tire vehicle). Always match or exceed the load index specified in your vehicle's owner manual or door jamb placard.

Common OEM sizes by vehicle class

These are representative sizes commonly fitted from the factory. Actual fitment varies by trim level, model year, and market. Always verify with your vehicle's door jamb placard or owner's manual.

For the interactive tire size calculator (sidewall height, overall diameter, circumference), see the Tire Size Calculator →. To convert between tire pressure units, see the Tire Pressure Converter →.