Tire Size Comparison Calculator
Use this calculator to compare two different tire sizes. Understanding the differences in overall diameter, sidewall height, and revolutions per mile can help you make informed decisions about tire changes, especially when considering aftermarket wheels or different tire profiles. This tool will also estimate your speedometer error if you change from Tire 1 to Tire 2.
Tire 1 (Original/Reference)
e.g., 205 for 205/55R16 e.g., 55 for 205/55R16 e.g., 16 for 205/55R16Tire 2 (New/Comparison)
e.g., 225 for 225/45R17 e.g., 45 for 225/45R17 e.g., 17 for 225/45R17Comparison Results
Tire 1 Details
Sidewall Height: 0.00 mm
Overall Diameter: 0.00 mm
Circumference: 0.00 mm
Revolutions per Mile: 0.00
Revolutions per Kilometer: 0.00
Tire 2 Details
Sidewall Height: 0.00 mm
Overall Diameter: 0.00 mm
Circumference: 0.00 mm
Revolutions per Mile: 0.00
Revolutions per Kilometer: 0.00
Comparison Summary
Overall Diameter Difference: 0.00 %
Speedometer Error: 0.00 %
Understanding Tire Size and Comparison
Tire sizes are typically displayed as a series of numbers and letters, like "205/55R16". Each part of this code provides crucial information about the tire's dimensions:
- Section Width (205): This is the width of the tire in millimeters, measured from sidewall to sidewall. A wider tire generally offers more grip but can affect fuel economy and steering feel.
- Aspect Ratio (55): This number represents the sidewall height as a percentage of the section width. In our example, the sidewall height is 55% of 205mm. A lower aspect ratio means a shorter sidewall, often found on performance tires, providing better handling but a harsher ride.
- Construction Type (R): "R" stands for Radial, the most common type of tire construction today.
- Rim Diameter (16): This is the diameter of the wheel rim in inches that the tire is designed to fit.
Why Compare Tire Sizes?
Comparing tire sizes is essential for several reasons:
- Speedometer Accuracy: Changing the overall diameter of your tires will directly impact your speedometer's accuracy. If the new tires have a larger diameter, your speedometer will read lower than your actual speed. If they have a smaller diameter, it will read higher. This can lead to speeding tickets or inaccurate mileage tracking.
- Vehicle Fitment: A new tire size might not fit your vehicle without rubbing against fenders, suspension components, or brake calipers, especially if the overall diameter or section width changes significantly.
- Performance and Handling: Changes in sidewall height and section width can alter your vehicle's handling characteristics, ride comfort, and even braking performance.
- Aesthetics: Many enthusiasts change tire and wheel sizes for a different look, but it's crucial to ensure functionality isn't compromised.
- Gear Ratio Impact: A change in tire diameter effectively changes your vehicle's final drive ratio, impacting acceleration and fuel economy. Larger tires will make your effective gear ratio "taller," potentially reducing acceleration but improving highway fuel economy (if the engine can handle the load).
How the Calculator Works
This calculator takes the section width, aspect ratio, and rim diameter for two tires and performs the following calculations:
- Sidewall Height: Calculated as (Section Width * Aspect Ratio / 100).
- Overall Diameter: This is the total height of the tire, calculated by adding the rim diameter (converted to millimeters) to twice the sidewall height.
- Circumference: The distance covered by one full rotation of the tire, calculated as Overall Diameter * Pi (approximately 3.14159).
- Revolutions per Mile/Kilometer: This indicates how many times the tire spins to cover one mile or kilometer, derived from the circumference.
- Overall Diameter Difference: The percentage difference between the overall diameters of Tire 1 and Tire 2.
- Speedometer Error: This calculates the percentage difference in speed reading. If the new tire (Tire 2) has a larger diameter than the original (Tire 1), your speedometer will read lower than your actual speed. Conversely, if Tire 2 is smaller, your speedometer will read higher.
Important Considerations
While this calculator provides valuable data, always consult a professional tire specialist before making significant changes to your vehicle's tire size. They can advise on proper fitment, load ratings, and potential impacts on your vehicle's safety systems (like ABS and traction control), which can sometimes be affected by significant tire size changes.