Tire Size Comparison Calculator
Use this calculator to compare two different tire sizes and understand how changing your vehicle's tires can affect key performance metrics like overall diameter, speedometer accuracy, and ground clearance.
Tire 1 (Original/Current)
Enter the specifications for your vehicle's current or original tire size.
The first number in a tire size (e.g., 205/55R16). The second number (e.g., 205/55R16), representing sidewall height as a percentage of the section width. The last number (e.g., 205/55R16), indicating the wheel size.Tire 2 (New/Proposed)
Enter the specifications for the new or proposed tire size you wish to compare.
The first number in a tire size (e.g., 225/45R17). The second number (e.g., 225/45R17), representing sidewall height as a percentage of the section width. The last number (e.g., 225/45R17), indicating the wheel size.Understanding Tire Sizes and Their Impact
Tire size is a critical factor in your vehicle's performance, safety, and even its appearance. Understanding the numbers on your tire's sidewall is the first step to making informed decisions about replacements or upgrades.
Decoding Tire Size Numbers (e.g., 205/55R16)
- 205 (Section Width in mm): This is the width of the tire in millimeters from sidewall to sidewall. A wider tire generally offers more grip but can increase rolling resistance and potentially rub against wheel wells.
- 55 (Aspect Ratio): This number represents the height of the tire's sidewall as a percentage of its section width. In our example, the sidewall height is 55% of 205mm. A lower aspect ratio means a shorter sidewall, often found on performance tires, offering better handling but a harsher ride.
- R (Construction Type): "R" stands for Radial, the most common type of tire construction today.
- 16 (Wheel Diameter in inches): This indicates the diameter of the wheel (rim) that the tire is designed to fit, measured in inches.
Why Compare Tire Sizes?
There are several reasons why you might want to compare tire sizes:
- Upgrading Wheels: If you're changing your wheel size (e.g., from 16-inch to 17-inch wheels), you'll need new tires that fit the larger diameter while maintaining a similar overall tire diameter to avoid issues.
- Performance Enhancement: Wider tires or lower aspect ratios can improve handling and cornering stability.
- Aesthetic Changes: Some drivers opt for larger wheels and tires for a more aggressive or customized look.
- Off-Roading: Larger overall diameter tires can increase ground clearance, beneficial for off-road vehicles.
- Fuel Economy: Significant changes in tire size can affect rolling resistance and vehicle gearing, impacting fuel efficiency.
Key Metrics Explained
Our calculator provides several key metrics to help you understand the differences between two tire sizes:
- Sidewall Height: The vertical distance from the wheel rim to the top of the tread. This directly impacts ride comfort and the tire's ability to absorb impacts.
- Overall Diameter: The total height of the tire from the ground to the top. This is crucial for speedometer accuracy and ground clearance.
- Circumference: The distance covered by one full rotation of the tire. This is directly related to speedometer readings.
- Revolutions per Mile: How many times the tire rotates to cover one mile. A higher number means the tire is smaller, and vice-versa.
- Speedometer Difference: This is one of the most important considerations. If your new tires have a different overall diameter than your original tires, your speedometer and odometer will no longer be accurate.
- Larger Tires: If your new tires are larger, your speedometer will read lower than your actual speed. For example, if it reads 60 mph, you might actually be going 62 mph. Your odometer will also under-report mileage.
- Smaller Tires: If your new tires are smaller, your speedometer will read higher than your actual speed. If it reads 60 mph, you might actually be going 58 mph. Your odometer will over-report mileage.
- Ground Clearance Change: The difference in overall diameter directly translates to a change in your vehicle's ground clearance. A larger diameter increases ground clearance, while a smaller one decreases it.
Example Comparison:
Let's use the default values in the calculator:
- Tire 1 (Original): 205/55R16
- Tire 2 (New): 225/45R17
When you calculate these, you'll find:
- Tire 1 Overall Diameter: Approximately 24.88 inches
- Tire 2 Overall Diameter: Approximately 24.97 inches
- Speedometer Difference: Approximately +0.36% (Tire 2 is slightly larger). This means if your speedometer reads 60 mph, your actual speed would be closer to 60.22 mph. This is a negligible difference.
- Ground Clearance Change: Approximately +0.04 inches (a very slight increase).
This example shows that moving from a 205/55R16 to a 225/45R17 keeps the overall diameter very close, which is often the goal when upgrading wheel sizes to maintain speedometer accuracy and avoid rubbing.
Always consult with a professional tire installer to ensure any new tire size is compatible with your vehicle's suspension, brakes, and wheel wells.
Comparison Results
"; resultsHTML += "| Metric | Tire 1 (Original) | Tire 2 (New) | Difference (T2 – T1) |
|---|---|---|---|
| Section Width | " + tire1Width.toFixed(0) + " mm | " + tire2Width.toFixed(0) + " mm | " + formatDifference(tire2Width – tire1Width, "mm") + " |
| Aspect Ratio | " + tire1Aspect.toFixed(0) + " % | " + tire2Aspect.toFixed(0) + " % | " + formatDifference(tire2Aspect – tire1Aspect, "%") + " |
| Wheel Diameter | " + tire1Wheel.toFixed(0) + " inches | " + tire2Wheel.toFixed(0) + " inches | " + formatDifference(tire2Wheel – tire1Wheel, "inches") + " |
| Sidewall Height | " + tire1SidewallInches.toFixed(2) + " inches (" + tire1SidewallMM.toFixed(0) + " mm) | " + tire2SidewallInches.toFixed(2) + " inches (" + tire2SidewallMM.toFixed(0) + " mm) | " + formatDifference(sidewallDifference, "inches") + " |
| Overall Diameter | " + tire1OverallDiameter.toFixed(2) + " inches | " + tire2OverallDiameter.toFixed(2) + " inches | " + formatDifference(diameterDifference, "inches") + " |
| Circumference | " + tire1Circumference.toFixed(2) + " inches | " + tire2Circumference.toFixed(2) + " inches | " + formatDifference(circumferenceDifference, "inches") + " |
| Revolutions per Mile | " + tire1RevsPerMile.toFixed(2) + " | " + tire2RevsPerMile.toFixed(2) + " | " + formatDifference(revsPerMileDifference, "") + " |