Wheel Tire Size Calculator
Use this calculator to compare your current tire size with a potential new size. Understand the impact on overall diameter, speedometer readings, and other critical metrics before making a change.
Original Tire Size (e.g., 205/55R16)
New Tire Size (e.g., 225/45R17)
Speedometer Reference
Understanding Your Tire Size
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:
- 205: Tire Width (mm) – This is the width of the tire in millimeters, measured from sidewall to sidewall.
- 55: Aspect Ratio (%) – This number represents the sidewall height as a percentage of the tire's width. In this example, the sidewall height is 55% of 205mm. A lower aspect ratio means a shorter sidewall.
- R: Construction Type – 'R' stands for Radial, which is the most common type of tire construction today.
- 16: Rim Diameter (inches) – This is the diameter of the wheel rim in inches that the tire is designed to fit.
Why Use a Tire Size Calculator?
Changing your vehicle's tire size, even slightly, can have several implications. A tire size calculator helps you understand these changes:
- Speedometer Accuracy: A different overall tire diameter will affect your speedometer and odometer readings. If the new tire is larger, your speedometer will read slower than your actual speed, and vice-versa.
- Vehicle Clearance: Larger tires might rub against fenders, suspension components, or other parts of your vehicle, especially during turns or over bumps.
- Handling Characteristics: Changes in sidewall height and tire width can alter your vehicle's handling, ride comfort, and steering response.
- Aesthetics: Many enthusiasts change tire sizes for a specific look, but it's important to ensure functionality isn't compromised.
- Fuel Economy: While often minor, significant changes in tire diameter or width can slightly impact fuel efficiency.
Key Metrics Explained
- Sidewall Height: The vertical distance from the wheel rim to the top of the tread. This directly impacts ride comfort and the tire's visual profile.
- Overall Diameter: The total height of the tire from the ground to the top. This is the most critical factor affecting speedometer accuracy and vehicle clearance.
- Circumference: The distance covered by the tire in one full rotation. Directly related to overall diameter.
- Revolutions Per Mile: How many times the tire rotates to cover one mile. A higher number means a smaller tire, and vice-versa.
Important Considerations When Changing Tire Sizes
When considering new tires, aim to keep the overall diameter within +/- 3% of the original tire's diameter to minimize issues. Beyond this range, you risk:
- Significant speedometer/odometer errors.
- Interference with vehicle components.
- Potential issues with Anti-lock Braking Systems (ABS) and Electronic Stability Control (ESC) systems, which rely on accurate wheel speed data.
- Changes in gear ratios, affecting acceleration and engine RPM at highway speeds.
- Impact on load capacity and speed ratings. Always ensure your new tires meet or exceed the vehicle manufacturer's recommendations.
- Tire Pressure Monitoring System (TPMS) recalibration may be necessary.
Always consult with a professional tire installer to ensure proper fitment and safety.
Calculation Results
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resultsHTML += "| Metric | Original Tire | New Tire | Difference |
|---|---|---|---|
| Tire Size Code | " + originalWidth + "/" + originalAspect + "R" + originalRim + " | " + newWidth + "/" + newAspect + "R" + newRim + " | |
| Sidewall Height | " + originalSidewallMM.toFixed(2) + " mm | " + newSidewallMM.toFixed(2) + " mm | " + (newSidewallMM – originalSidewallMM).toFixed(2) + " mm |
| Overall Diameter | " + originalOverallDiameterInches.toFixed(2) + " inches (" + originalOverallDiameterMM.toFixed(2) + " mm) | " + newOverallDiameterInches.toFixed(2) + " inches (" + newOverallDiameterMM.toFixed(2) + " mm) | " + diameterDifferencePercent.toFixed(2) + "% |
| Circumference | " + originalCircumferenceInches.toFixed(2) + " inches | " + newCircumferenceInches.toFixed(2) + " inches | " + circumferenceDifferencePercent.toFixed(2) + "% |
| Revolutions Per Mile | " + originalRevsPerMile.toFixed(2) + " | " + newRevsPerMile.toFixed(2) + " | " + revsPerMileDifferencePercent.toFixed(2) + "% |