Tire Size Calculator
Compare tire sizes and see how different tires affect your speedometer, ground clearance, and odometer. Enter two tire sizes to see the differences.
Enter Tire Sizes
Visual Comparison
17"
16"
Diameter & Circumference
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Original Diameter
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Replacement Diameter
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Diameter Difference
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Diameter Change %
Speedometer Impact
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Speedometer Error at 60 mph
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Speedometer Shows
60 mph
Actual Speed
Revolutions & Clearance
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Original Rev/Mile
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Replacement Rev/Mile
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Rev/Mile Difference
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Ground Clearance Change
Detailed Measurements
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Original Sidewall
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Replacement Sidewall
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Original Circumference
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Replacement Circumference
Frequently Asked Questions
How do I read a tire size like 225/65R17?▾
The first number (225) is the tire width in millimeters. The second number (65) is the aspect ratio, meaning the sidewall height is 65% of the width. R means radial construction, and 17 is the rim diameter in inches.
How does changing tire size affect my speedometer?▾
A larger tire covers more ground per revolution, so your speedometer will read lower than your actual speed. A smaller tire does the opposite, making your speedometer read higher than actual speed.
What is the maximum tire size difference I should consider?▾
Most experts recommend staying within 3% of the original tire diameter to avoid speedometer errors, clearance issues, and drivetrain stress. This calculator shows the exact percentage difference to help you decide.
Does tire size affect fuel economy?▾
Yes. Larger, heavier tires generally increase rolling resistance and reduce fuel economy. Smaller tires may improve MPG slightly but can affect handling and ride comfort.
Is this tire size calculator free to use?▾
Yes. This tire size comparison tool is completely free, runs in your browser, and requires no signup. No data is sent to any server.