A quick guide to understanding the numbers and letters on your tire sidewall.
The markings on your tire sidewall look like a code — but once you know what they mean, they tell you everything about your tire’s size, capacity, and speed rating.
1. Breaking Down the Numbers
Take a marking like 205/55R16 91V. The 205 is the tire width in millimeters. The 55 is the aspect ratio — the sidewall height as a percentage of the width. R means radial construction (standard for all modern tires). And 16 is the rim diameter in inches.
2. Load Index and Speed Rating
The 91 is the load index — the maximum weight each tire can carry (in this case, 615 kg). The V is the speed rating — the maximum speed the tire is designed for (240 km/h). You should always match or exceed your car manufacturer’s recommended ratings. You can always look up the load index and speed rating tables to find the meaning of each symbol.
3. The DOT Date Code
Look for a four-digit number near the DOT marking. It tells you when the tire was made. For example, 0525 means week 5 of 2025. This is important because tires age even when not in use — avoid buying tires that have been sitting in stock for more than 4 [RO1] years.
4. Why This Matters When Buying
When replacing tires, always match the size specified in your owner’s manual or on the driver’s door sticker. Using the wrong size affects speedometer accuracy, handling, and can even damage your suspension. At Round One, we always verify the correct size for your vehicle before fitting.