How to Read Tire Sizes: A Step‑by‑Step Guide to Tire Codes

Understanding how to read tire sizes is essential whether you're replacing tires, upgrading for performance, or trying to interpret the tire code on your sidewall. This guide breaks down the tire size format step-by-step so you can confidently choose the correct tires for your vehicle.

What Is a Tire Size?

A tire size is a standardized code printed on the sidewall of every tire. It provides essential information about the tire’s dimensions, construction, and compatibility. A typical tire size looks like this: 225/65R17 102H. Each part of this code gives specific details about the tire's capabilities and fit.

Breaking Down the Tire Code

Here’s a detailed explanation of what each component of a standard tire size means:

  • 225: This is the width of the tire in millimeters from sidewall to sidewall.
  • 65: The aspect ratio, which represents the height of the sidewall as a percentage of the width.
  • R: Indicates radial construction, which is the standard type for modern tires.
  • 17: The wheel diameter the tire is designed to fit, measured in inches.
  • 102: The load index, representing the maximum load the tire can safely carry.
  • H: The speed rating, showing the maximum speed the tire can handle safely.

Step-by-Step Guide to Reading a Tire Size

1. Locate the Tire Size

Look on the sidewall of your current tire. The full code may appear like this: P215/60R16 94T. It may start with a letter, which sometimes indicates vehicle type:

  • P: Passenger vehicle
  • LT: Light truck
  • T: Temporary or spare tire

2. Understand the Tire Width

The first number after the letter (if present) is the width in millimeters. In 215/60R16, the tire is 215 mm wide. This affects traction and how much road contact the tire makes.

3. Analyze the Aspect Ratio

The second number (after the slash) is the aspect ratio. It tells you how tall the sidewall is as a percentage of the tire’s width. For example, a 60 means the height is 60% of 215 mm.

4. Check the Construction Type

Most modern tires use radial construction, marked with an “R.” This means the tire layers run radially across the tire, providing better durability and performance.

5. Identify the Wheel Diameter

This is the inner diameter of the tire, or the size of the rim it fits, measured in inches. A 16 means it fits a 16-inch wheel.

6. Understand the Load Index

The load index is a number that corresponds to a specific weight capacity. For example, a load index of 94 means the tire can support 1,477 pounds. You can reference load index charts online for exact values.

7. Read the Speed Rating

The final letter indicates the maximum speed the tire can handle. For example, “T” is rated up to 118 mph, while “H” is rated up to 130 mph. Always choose a rating that matches or exceeds your vehicle’s requirement.

Why Reading Tire Sizes Matters

  • Safety: Using the correct tire size ensures optimal handling and braking performance.
  • Fuel Efficiency: The wrong size can affect your car's fuel economy.
  • Speedometer Accuracy: Tire diameter impacts how your speedometer reads.
  • Warranty and Insurance: Some warranties and policies require OEM-compliant tire sizes.

Tips for Choosing the Right Tire Size

  • Use your vehicle’s owner’s manual or door jamb sticker as the primary reference.
  • Use an online tire size calculator to compare alternate sizes safely.
  • Stick to within 3% of your original tire’s overall diameter when upgrading.
  • Consult a tire professional before switching to a non-standard size.

Helpful Tools: Try a Tire Size Calculator

Use the Tire Size Conversion Calculator to quickly compare sizes, understand diameters, and convert between metric and inch formats. It’s especially useful for off-roaders, tuners, and anyone replacing their wheels or tires.

Common Tire Code Mistakes

  • Ignoring load and speed ratings: Don’t just match the size—match performance ratings too.
  • Assuming “bigger is better”: Oversized tires can rub against wheel wells and throw off your speedometer.
  • Not accounting for aspect ratio: A low-profile tire may not absorb bumps as well as a higher sidewall.

Conclusion

Learning how to read tire sizes empowers you to make smarter, safer decisions about your vehicle. By understanding the meaning behind tire codes, you avoid costly mistakes and get the most out of your driving experience. Bookmark this guide, or use our free calculator tool anytime you're shopping for new tires.

Scroll to Top