Tire Size Comparison Calculator
Use this calculator to compare your original tire size with a potential new tire size. Understand the impact on overall diameter, circumference, and speedometer accuracy.
Original Tire Size
New Tire Size
Tire Comparison Results
Original Tire (${originalWidth}/${originalAspect}R${originalWheel}):- Overall Diameter: ${originalTireDiameter_inches.toFixed(2)} inches
- Circumference: ${originalTireCircumference_inches.toFixed(2)} inches
- Revolutions per Mile: ${originalRevsPerMile.toFixed(2)}
- Overall Diameter: ${newTireDiameter_inches.toFixed(2)} inches
- Circumference: ${newTireCircumference_inches.toFixed(2)} inches
- Revolutions per Mile: ${newRevsPerMile.toFixed(2)}
- Diameter Difference: 0.01 || diameterDifference_percent ${diameterDifference_percent.toFixed(2)}% ${diameterDiffText}
- Circumference Difference: 0.01 || circumferenceDifference_percent ${circumferenceDifference_percent.toFixed(2)}% ${circumferenceDiffText}
Understanding and Using a Tire Size Calculator
Changing your vehicle's tires is a common practice, whether for aesthetic upgrades, performance enhancements, or simply replacing worn-out rubber. However, altering tire dimensions from the manufacturer's specifications can have significant implications. A tire size calculator is an indispensable tool that helps you understand these changes before making a purchase.
Decoding Tire Sizes: What Do the Numbers Mean?
Tire sizes are typically displayed in a standardized format, such as 205/55R16. Let's break down what each part signifies:
- 205 (Tire Width in Millimeters): This is the width of the tire from sidewall to sidewall, measured in millimeters. A wider tire generally offers more grip but can also increase rolling resistance.
- 55 (Aspect Ratio): This number represents the sidewall height as a percentage of the tire's width. In this example, the sidewall height is 55% of 205mm. A lower aspect ratio means a shorter sidewall, often found on performance tires, providing better handling but potentially a harsher ride.
- R (Construction Type): The 'R' stands for Radial, indicating the tire's internal construction. Almost all modern passenger vehicle tires are radial.
- 16 (Wheel Diameter in Inches): This number specifies the diameter of the wheel (or rim) that the tire is designed to fit, measured in inches.
Why Use a Tire Size Calculator?
When considering a new set of tires, especially if you're changing wheel sizes or opting for a different profile, a calculator helps you:
- Maintain Speedometer Accuracy: This is perhaps the most critical reason. Your vehicle's speedometer and odometer are calibrated based on the original tire's overall diameter and circumference. Changing these dimensions will cause your speedometer to read incorrectly, leading to either under-reporting or over-reporting your actual speed.
- Prevent Clearance Issues: A significantly larger tire diameter or width might cause the tire to rub against your vehicle's fenders, suspension components, or brake calipers, especially during turns or over bumps.
- Assess Ride Quality: Tires with a lower aspect ratio (shorter sidewall) generally offer a sportier feel and improved cornering but can result in a firmer, less comfortable ride.
- Understand Performance Impact: Changes in tire size can affect acceleration, braking distances, and fuel economy. Larger, heavier tires can increase unsprung weight, potentially reducing fuel efficiency and slowing acceleration.
- Ensure Safety: Incorrect tire sizes can compromise handling, stability, and braking performance, posing a safety risk.
How the Calculator Works
Our calculator takes your original tire's width, aspect ratio, and wheel diameter, along with the same measurements for your proposed new tire. It then performs the following calculations:
- Overall Tire Diameter: This is the total height of the tire when mounted and inflated. It's calculated by adding the wheel diameter to twice the sidewall height.
- Tire Circumference: The distance covered by one full rotation of the tire. This is directly proportional to the overall diameter.
- Revolutions Per Mile: How many times the tire rotates to cover one mile. This is crucial for speedometer and odometer accuracy.
- Diameter and Circumference Difference (%): Shows the percentage difference between your original and new tires. A difference of more than 3% is generally considered significant and can lead to noticeable issues.
- Speedometer Error: This is a direct result of the circumference difference. If your new tires have a larger circumference, your vehicle will travel further per rotation, meaning your actual speed will be higher than what your speedometer indicates. Conversely, smaller new tires will result in your actual speed being lower than the speedometer reading.
Important Considerations When Changing Tire Sizes
- Manufacturer Recommendations: Always consult your vehicle's owner's manual or the tire placard (usually located on the driver's side door jamb) for recommended tire sizes.
- Professional Advice: If you're unsure, consult with a reputable tire specialist or mechanic. They can provide expert advice on fitment and potential issues.
- TPMS Recalibration: If your vehicle has a Tire Pressure Monitoring System (TPMS), changing tire sizes might require recalibration or new sensors.
- Load Index and Speed Rating: Ensure your new tires meet or exceed the load index and speed rating requirements for your vehicle.
By using this tire size calculator, you can make informed decisions about tire replacements or upgrades, ensuring your vehicle remains safe, performs optimally, and maintains accurate speed readings.