1. What is a Tyre Size Comparison Calculator?

Definition: This calculator compares two tyre sizes and shows the difference in diameter, both in millimeters and as a percentage.

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

2. How Does the Calculator Work?

The calculator uses the formula:

Where diameter is calculated as: \[ \text{Diameter} = \left(\frac{\text{Width} \times \text{Aspect Ratio}}{100} \times \frac{2}{25.4}\right) + \text{Rim Size} \]

Explanation: The calculator converts the tyre width and sidewall height to inches, adds the rim diameter, then compares the two sizes.

3. Importance of Tyre Size Comparison

Details: Proper tyre size comparison ensures your speedometer remains accurate, maintains proper gearing, and prevents clearance issues.

4. Using the Calculator

Tips: Enter the width in mm, aspect ratio as a percentage, and rim diameter in inches for both old and new tyre sizes.

5. Frequently Asked Questions (FAQ)

Q1: What does a positive delta mean?
A: A positive delta means your new tyres are larger than the old ones, which will make your speedometer read slower than actual speed.

Q2: How much difference is acceptable?
A: Generally, differences under 3% are considered acceptable for most vehicles.

Q3: Why does Australia use this format?
A: Australia uses the metric system for tyre width but retains inches for rim diameters, following international tyre sizing standards.

Q4: Does this affect fuel economy?
A: Yes, larger tyres typically decrease fuel economy due to increased rolling resistance and changed gearing.

Q5: How do I find my current tyre size?
A: Look on the sidewall of your tyre for numbers like "205/55R16" where 205 is width, 55 is aspect ratio, and 16 is rim diameter.