Compare tire sizes and calculate diameter, circumference, and speedometer differences
Tire size is indicated by a series of numbers and letters on the tire sidewall, such as 225/65R17. The first number (225) represents the tire width in millimeters, the second number (65) is the aspect ratio (sidewall height as a percentage of width), and the final number (17) is the rim diameter in inches.
When changing tire sizes, it's crucial to maintain a similar overall diameter to avoid speedometer inaccuracy, potential drivetrain issues, and clearance problems. Generally, staying within ±3% of the original diameter is recommended.
Larger tires cover more ground per revolution, causing your speedometer to read slower than actual speed. Smaller tires have the opposite effect. A 3% difference means at 60 mph, your actual speed could be 58.2 mph or 61.8 mph.
Wider tires increase rolling resistance and weight, potentially reducing fuel economy. Taller tires can improve highway efficiency but may reduce acceleration. The impact varies based on driving conditions and vehicle type.
Wider tires generally provide better grip and cornering, while narrower tires can improve steering response. Lower aspect ratios offer better handling but a firmer ride. Consider your driving priorities when selecting tire sizes.
Larger tires may rub against fenders, suspension components, or the frame, especially during turns or over bumps. Always verify fitment with your vehicle's specifications and consider suspension modifications if necessary.
| Change Type | Example | Benefits | Considerations |
|---|---|---|---|
| Plus Sizing | 225/65R17 → 235/55R18 | Better handling, sportier look | Firmer ride, higher cost |
| Wider Tires | 225/65R17 → 245/65R17 | Improved traction, stability | Reduced fuel economy, clearance |
| Taller Tires | 225/65R17 → 225/70R17 | Better ground clearance, comfort | May affect handling, clearance |
| Lower Profile | 225/65R17 → 225/55R17 | Sharper handling, appearance | Harsher ride, wheel damage risk |
Always consult your vehicle's owner manual or the tire placard (usually on the driver's door jamb) for recommended tire sizes. These recommendations are based on extensive testing for safety, performance, and efficiency specific to your vehicle.
When changing tire sizes, ensure the new tires meet or exceed the load index and speed rating of your original tires. Using tires with insufficient ratings can be dangerous and may void warranties or insurance coverage.
For optimal performance and safety, all four tires should be the same size, brand, and model when possible. Mixing tire sizes can affect handling, traction control systems, and all-wheel drive functionality. Some vehicles allow different front and rear sizes (staggered fitment), but this should match manufacturer specifications.
Tire Pressure Monitoring Systems (TPMS) may need recalibration after changing tire sizes. Significant size changes can affect TPMS accuracy and may trigger warning lights. Consult a professional for proper TPMS setup with new tire sizes.