Tire Size Calculator
Compare tire sizes, calculate speedometer differences, and find equivalent tire sizes for your vehicle with our advanced tire size calculator.
Tire Size Comparison
Calculating tire size differences…
Tire Size Comparison Results
Detailed Comparison
| Specification | Current Tire | New Tire | Difference |
|---|---|---|---|
| Tire Size | 225/45R17 | 235/45R18 | – |
| Section Width | 225 mm | 235 mm | +10 mm |
| Aspect Ratio | 45% | 45% | 0% |
| Rim Diameter | 17″ | 18″ | +1″ |
| Tire Diameter | 25.0″ | 25.4″ | +0.4″ |
| Circumference | 78.5″ | 79.8″ | +1.3″ |
| Revolutions per Mile | 809 | 795 | -14 |
Frequently Asked Questions
Tire size markings follow a standard format like “225/45R17”. The first number (225) is the width of the tire in millimeters. The second number (45) is the aspect ratio, which is the height of the sidewall as a percentage of the width. The “R” indicates radial construction, and the final number (17) is the diameter of the wheel rim in inches. Understanding these markings helps you select the right tires for your vehicle.
Changing tire size affects your speedometer accuracy because it changes the overall diameter of your wheel. Larger diameter tires cover more ground per revolution, causing your speedometer to read slower than your actual speed. Smaller diameter tires have the opposite effect. Our calculator shows you the exact difference so you can understand how much your speedometer will be affected.
Generally, a difference of up to 3% in tire diameter is considered acceptable without affecting vehicle performance or safety. Differences larger than 3% can cause issues with speedometer accuracy, ABS system performance, transmission shifting, and can potentially cause rubbing against fenders or suspension components. Always consult with a tire professional before making significant changes to your tire size.
Using different tire sizes on front and rear (staggered fitment) is common on performance cars and some trucks. However, this should only be done if specifically recommended by the vehicle manufacturer. For most vehicles, especially those with all-wheel drive or traction control systems, it’s important to maintain the same overall tire diameter on all four wheels to avoid damaging the drivetrain.
Plus sizing involves increasing wheel diameter while decreasing tire aspect ratio to maintain approximately the same overall tire diameter. For example, changing from 16″ wheels with 65-series tires to 17″ wheels with 55-series tires. This allows for larger wheels and improved handling while maintaining speedometer accuracy and avoiding clearance issues. Our calculator helps you find compatible plus size options.