Free Tire Size Calculator: Compare Dimensions & Find the Perfect Fit
Compare tire dimensions, calculate speedometer accuracy, and find the perfect fit for your vehicle
Popular Tire Size Comparisons
Current Tire
225/65R17
New Tire
245/55R18
Tire Size Comparison Results
Visual Comparison
Current: 225/65R17
Diameter: 28.52 inches
New: 245/55R18
Diameter: 28.61 inches
Note: Visual comparison is to scale but size is relative
Diameter Difference
+0.09 in
(+0.33%)
Speedometer Error
-0.33%
Speedometer reads higher than actual speed
Revolutions Per Mile
-2
New: 705 | Current: 707
Detailed Comparison
| Measurement | Current Tire | New Tire | Difference | % Change |
|---|---|---|---|---|
| Overall Diameter | 28.52 in | 28.61 in | +0.09 in | +0.33% |
| Section Width | 225 mm (8.86 in) | 245 mm (9.65 in) | +0.79 in | +8.89% |
| Sidewall Height | 5.76 in | 5.31 in | -0.45 in | -7.86% |
| Circumference | 89.58 in | 89.88 in | +0.30 in | +0.33% |
| Revolutions Per Mile | 707 | 705 | -2 | -0.33% |
Speedometer Impact Analysis
With your new tire size, your speedometer will read 0.33% higher than your actual speed.
Speedometer reads:
- 30 mph = 30.1 mph actual
- 45 mph = 45.1 mph actual
- 60 mph = 60.2 mph actual
When you're going:
- 30 mph actual = 29.9 mph on speedometer
- 45 mph actual = 44.9 mph on speedometer
- 60 mph actual = 59.8 mph on speedometer
Understanding Tire Sizes and Their Impact
Tire sizes are represented using a standardized format that includes the width, aspect ratio, and rim diameter. For example, in a tire size of 225/65R17:
- 225 represents the width of the tire in millimeters from sidewall to sidewall
- 65 is the aspect ratio, which is the height of the sidewall as a percentage of the width
- R indicates that it's a radial tire (the most common type today)
- 17 is the diameter of the wheel/rim in inches
Changing your tire size can affect various aspects of your vehicle's performance:
- Speedometer Accuracy: Your vehicle's speedometer is calibrated based on the original tire size. Changes in overall diameter will affect its accuracy.
- Handling: Wider tires generally provide better grip, while taller sidewalls can absorb bumps better but may reduce cornering precision.
- Ground Clearance: Larger diameter tires will increase your vehicle's ground clearance.
- Fuel Economy: Heavier or wider tires can increase rolling resistance and reduce fuel efficiency.
- Fitment: Larger tires may rub against fenders or suspension components, especially during turning or when the suspension compresses.
Our tire size calculator helps you understand these changes before making a purchase, ensuring you select the right tire size for your vehicle and driving needs.
Frequently Asked Questions
What is the "plus-sizing" method for tire upgrades?
Plus-sizing is a method of upgrading tires where you increase the wheel diameter while decreasing the sidewall height, maintaining approximately the same overall tire diameter. For example, going from 215/65R16 to 225/55R17 keeps similar overall diameter but provides a wider tire with a lower profile.
How much speedometer error is acceptable?
Generally, a speedometer error of less than 3% is considered acceptable for most vehicles. Beyond this, you might want to consider recalibrating your speedometer or being consistently aware of the correction factor needed when reading your speed.
Will changing my tire size affect my vehicle's fuel economy?
Yes, tire size changes can affect fuel economy. Heavier tires, increased rolling resistance from wider tires, and taller tires can all decrease fuel efficiency. Generally, keeping close to the original overall diameter helps minimize fuel economy impacts.
Can I put different size tires on the front and rear of my vehicle?
Some sports cars and performance vehicles come with staggered setups from the factory, with wider tires on the rear. However, for most vehicles, it's recommended to maintain the same size on all positions unless the manufacturer specifically recommends a staggered setup.
How do winter tires typically differ in size from summer or all-season tires?
Winter tires often come in narrower widths than summer or all-season tires to provide better performance in snow. A narrower tire cuts through snow more effectively and provides better traction. Some drivers choose to downsize the wheel diameter and increase sidewall height for winter driving.
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