How to Read Tire Sizes: A Complete Guide

When it comes time to replace your tires, the sequence of numbers and letters on the sidewall can seem like a secret code. But understanding how to read tire sizes is crucial for ensuring proper fitment, safety, and performance for your vehicle.

Let's break down a common tire size: 225/45R17.

1. Section Width (225)

The first number, 225, is the width of the tire measured in millimeters from sidewall to sidewall. A wider tire generally provides more grip and stability on dry roads, but it may also decrease fuel efficiency due to increased rolling resistance.

2. Aspect Ratio (45)

The second number, 45, is the aspect ratio. This is a percentage that tells you how tall the sidewall is compared to the tire's width. In this example, the sidewall height is 45% of 225mm.

• Lower aspect ratios (e.g., 30, 35, 40) mean shorter, stiffer sidewalls, which improve handling and cornering but can result in a harsher ride.
• Higher aspect ratios (e.g., 65, 70, 75) mean taller sidewalls, which absorb bumps better and provide a smoother ride, commonly found on SUVs and trucks.

3. Construction (R)

The letter R stands for Radial. This refers to the internal construction of the tire. Over 98% of modern tires are radial, meaning the internal cord plies run at 90 degrees to the direction of travel.

4. Wheel Diameter (17)

The final number, 17, is the diameter of the wheel (or rim) that the tire is designed to fit, measured in inches. If you have 17-inch wheels, you must buy tires that end in 17.

Thinking of Changing Your Tire Size?

If you want to upgrade your wheels or change your tire width, you need to ensure the overall diameter stays within a safe 3% margin to avoid breaking your speedometer or rubbing your suspension.

Use our visual 3D Tire Size Calculator below to compare your factory tires with your desired upgrade instantly!