Date Posted: Aug 28, 2026

How to Read and Understand Different Tire Sizes | Pete Smith Auto

A tire size can look like a string of random characters, but each part provides useful information about the tire’s dimensions and construction. Understanding tire sizes can help you choose the right replacement tires and compare options, while knowing what to look for. Here’s a simple breakdown of how to read the info on your tire’s sidewall — and how to choose the right size for your vehicle.

Breaking Down a Tire Size

Let’s use 225/65R17 102H as an example. Each part tells you something different about the tire:

• 225: Tire’s width in millimeters
• 65: Aspect ratio or sidewall height compared with the tire’s width
• R: Radial construction
• 17: Wheel diameter in inches
• 102: Load index that indicates how much weight the tire can support
• H: Speed rating that indicates the tire’s maximum rated speed

The first three numbers and letters are usually the easiest to spot. Together, they describe the tire’s basic size and construction.

What is the Meaning of Tire Width?

The first number is the width in millimeters from one sidewall to the other. So, seeing the number 225 indicates a 225 mm width. A wider tire can affect how your vehicle feels on the road — but choosing a different width isn’t simply a matter of preference. Your vehicle is designed around specific tire dimensions, so follow the manufacturer’s recommendations when replacing tires.

What Does the Tire Aspect Ratio Mean?

The second number is the aspect ratio: how high the sidewall is as a certain percent of the width. For a 225/65 tire, the sidewall height is 65% of 225 millimeters. Higher ratios usually mean taller sidewalls, and lower ratios often mean shorter sidewalls. This measurement can influence certain vehicle factors, such as ride comfort, handling, and overall appearance.

What Do the Other Numbers and Letters Mean?

The remaining characters provide info about how the tire’s constructed and how it’s designed to perform.

• R: Most modern passenger tires use radial construction.
• Wheel diameter: This tells you the diameter of the wheel the tire fits, so a 17-inch tire, for example, is designed for a 17-inch wheel.
• Load index: This is the specific maximum load capacity and should match your vehicle’s requirements.
• Speed rating: The letter indicates the maximum speed the tire’s rated to sustain under specified conditions.

You may also see additional markings on the sidewall for other characteristics — winter tires, all-season tires, reinforced construction. These markings vary depending on the tire.

How to Find the Right Tire Size for Your Vehicle

The tire currently installed on your vehicle isn’t the only place to check for the correct size. Your owner’s manual and the tire information placard, commonly found inside the driver’s door, can provide the manufacturer-recommended specifications. When shopping for replacement tires, make sure the size and load capacity, along with the speed rating, are appropriate for your vehicle.

If you’re searching for tire repair near me, it’s also worth having a professional inspect your tires before deciding whether they need repair or replacement. A qualified tire repair service can check for issues that may not be obvious at a glance.

Get Help Choosing the Right Tires

Tire sizes may seem confusing at first — but once you know what each number and letter represents, the info becomes much easier to understand. Our team at Pete Smith Auto can provide additional guidance if you have questions about your vehicle’s tire size or need help understanding your options.

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