How to Read a Tire Size and Why It Matters
How to Read a Tire Size and Why It Matters
Decode the numbers on your tire sidewall and understand how they affect your ride.
Breaking Down the Code
A tire size like 225/45R17 packs three key numbers into a short code. The first number, 225, is the tire’s width in millimeters. The second number, 45, is the aspect ratio, meaning the sidewall height as a percentage of the width. The final number, 17, is the wheel diameter in inches.
Why Overall Diameter Matters
Two tires with different width and aspect ratio numbers can still end up with a similar overall diameter. Overall diameter affects your speedometer accuracy, gearing, and how much clearance your vehicle has, which is why it’s worth comparing rather than just looking at the wheel size.
Changing Tire Sizes Safely
If you’re considering a different tire size than the factory specification, many mechanics recommend staying within about 3 percent of the original overall diameter to avoid throwing off your speedometer and other vehicle systems.
When in Doubt, Compare
Before buying new tires in a different size, calculating and comparing the overall diameter and circumference of your current and prospective tires can help you avoid an expensive fitting mistake.