Compare Tire Sizes Before You Buy
Upgrading your vehicle to larger wheels or wider tires completely alters its geometry. If you change the overall diameter of your tires without doing the math, your speedometer will read incorrectly, and the tires may scrape against your fenders. Our Tire Size Calculator instantly translates complex metric tire codes into physical dimensions for perfect fitment.
Decoding the Sidewall Numbers
A tire code like 225/45R17 is incredibly confusing because it mixes the metric system, percentages, and inches into one string. Here is how to read it:
- 225 (Width): The width of the tire tread measured in millimeters (from sidewall to sidewall).
- 45 (Aspect Ratio): This is a percentage, not a measurement. It means the height of the sidewall is 45% of the tire's width (225mm). A lower number (e.g., 30) means a very thin, low-profile tire.
- R17 (Wheel Diameter): The 'R' stands for Radial construction. The '17' is the diameter of the metal wheel (rim) measured in inches.
- The Danger of Upsizing: If you install a tire with a larger overall diameter, your tire will rotate slightly slower at a given speed. This means when your speedometer says you are driving 60 MPH, you might actually be driving 65 MPH, leading to speeding tickets.
How to Use This Tool
- Upload or Input Data: Select your file or paste your data directly into the tool interface. Everything remains on your device.
- Configure & Process: Adjust any optional settings if necessary. The tool will process your data instantly inside your browser.
- Download Result: Preview the output and click the download or copy button to save your final results.
Frequently Asked Questions
What is the maximum tire size I can upgrade to?
The general rule of thumb is the '3% Rule'. You should never install a tire with an overall diameter that is more than 3% larger or smaller than your car's factory OEM tire. Exceeding 3% can damage anti-lock brakes (ABS) and transmission gearing.
What is 'Plus Sizing' (Plus 1, Plus 2)?
Plus sizing is upgrading to a larger metal wheel (e.g., from a 17-inch to an 18-inch rim) while keeping the overall tire diameter identical to factory specs. To achieve this, as the metal wheel gets bigger, the rubber sidewall must get thinner.
Why does a wider tire decrease fuel economy?
Wider tires (e.g., moving from a 215 to a 245) create a larger 'contact patch' with the road. While this massively improves cornering grip and braking distance, it also increases rolling resistance and aerodynamic drag, which lowers MPG.