Compare two tire sizes to see differences in diameter, circumference, and speedometer accuracy. Perfect for upgrading wheels or finding equivalent size replacements.
225/55R17
235/45R18
Tire sizes are expressed in a standardized format like 225/55R17, where each number represents a crucial dimension. The first number (225) is the tire width in millimeters from sidewall to sidewall. The second number (55) is the aspect ratio—the sidewall height as a percentage of the width. The “R” indicates radial construction, and the final number (17) is the wheel diameter in inches.
Understanding these dimensions is crucial when upgrading wheels or replacing tires. The overall diameter affects your speedometer accuracy, odometer readings, and vehicle clearance. Most manufacturers recommend keeping tire size changes within 3% of the original diameter to avoid adverse effects on handling, braking, and drivetrain components.
Speedometer & Odometer
Larger tires make your speedometer read slower than actual speed. A 3% larger tire at an indicated 60 mph means you're actually traveling at 61.8 mph. This also affects odometer readings and fuel economy calculations.
Ground Clearance
Each inch of tire diameter increases ground clearance by half an inch. This matters for off-road vehicles but can affect handling and center of gravity for street cars. Check for fender clearance before upsizing.
Acceleration & Braking
Larger tires effectively lower your gear ratio, potentially reducing acceleration but improving highway efficiency. ABS and stability control calibration may be affected by significant size changes.
Ride Quality
Lower aspect ratio tires (shorter sidewalls) provide sharper handling but a firmer ride. Higher aspect ratios absorb more bumps but may feel less responsive in corners. Balance comfort and performance for your needs.
Plus sizing is the practice of increasing wheel diameter while maintaining overall tire diameter by reducing sidewall height. For example, upgrading from 205/55R16 to 225/45R17 maintains nearly the same overall diameter while providing a sportier appearance and improved handling through a wider tread and shorter sidewall.
The standard plus-sizing increments are: Plus One (+1" wheel, -10 aspect ratio), Plus Two (+2" wheel, -20 aspect ratio), and so on. Always verify the overall diameter stays within 3% of original spec using this calculator before purchasing. Also check that the new width won't cause rubbing on suspension components or fenders.
| Original Size | Plus One | Plus Two |
|---|---|---|
| 205/55R16 | 225/45R17 | 235/40R18 |
| 225/55R17 | 245/45R18 | 255/40R19 |
| 245/45R18 | 265/35R19 | 275/30R20 |
Note: Always verify tire fitment with your vehicle manufacturer or tire shop. This calculator provides dimensional comparisons but doesn't account for wheel width compatibility or vehicle-specific clearance issues.