1. What is a Tyre Size Comparison Calculator?

Definition: This calculator compares the diameters of two different tyre sizes to show their differences in inches and percentage.

Purpose: It helps vehicle owners and mechanics understand how different tyre sizes will affect speedometer accuracy, gearing, and vehicle clearance.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( D \) — Overall diameter (inches)
• \( W \) — Tyre width (millimeters)
• \( AR \) — Aspect ratio (percentage of width)
• \( R \) — Rim diameter (inches)

Explanation: The sidewall height is calculated (width × aspect ratio), converted to inches, doubled (for top and bottom sidewalls), then added to rim diameter.

3. Importance of Tyre Size Comparison

Details: Comparing tyre sizes ensures proper fitment, maintains speedometer accuracy, and prevents rubbing or clearance issues.

4. Using the Calculator

Tips: Enter the width in mm, aspect ratio as a percentage (e.g., 55 for 55%), and rim diameter in inches for both tyres you want to compare.

5. Frequently Asked Questions (FAQ)

Q1: What's considered a significant difference in tyre diameter?
A: Generally, differences over 3% may affect speedometer accuracy and vehicle performance.

Q2: How does tyre diameter affect my speedometer?
A: Larger tyres make the speedometer read slower than actual speed, smaller tyres make it read faster.

Q3: Can I use this for plus-sizing calculations?
A: Yes, this helps determine proper plus-size combinations that maintain similar overall diameters.

Q4: What's the 25.4 in the formula?
A: This converts millimeters to inches (1 inch = 25.4 mm).

Q5: Does this account for tyre wear?
A: No, this calculates theoretical new tyre diameters. Worn tyres will be slightly smaller.