1. What is a Tyre Size Speed Calculator?

Definition: This calculator determines how changing tyre sizes affects your vehicle's speedometer reading and actual speed.

Purpose: It helps vehicle owners understand the impact of tyre size changes on speed measurement and vehicle performance.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• Speed Factor — The multiplier for your speed (dimensionless)
• New Diameter — Diameter of new tyres (mm)
• Old Diameter — Diameter of original tyres (mm)

Explanation: When you install larger tyres, your speedometer will under-read (show slower than actual speed). Smaller tyres cause the speedometer to over-read.

3. Importance of Tyre Size Calculations

Details: Correct tyre size calculations ensure accurate speed readings, proper gearing, and prevent potential legal issues from incorrect speedometer readings.

4. Using the Calculator

Tips: Measure or look up the diameters of both your old and new tyres in millimeters. Enter both values to calculate the speed factor.

5. Frequently Asked Questions (FAQ)

Q1: How do I find my tyre diameter?
A: Check manufacturer specifications or use a tyre size calculator that converts tyre codes (e.g., 205/55R16) to diameter.

Q2: What does the speed factor mean?
A: Multiply your speedometer reading by this factor to get your actual speed. A factor of 1.05 means you're going 5% faster than shown.

Q3: Does this affect odometer readings?
A: Yes, the same factor applies to distance measurements. Larger tyres will cause the odometer to under-report distance traveled.

Q4: Is wheel width important for this calculation?
A: Only indirectly, as it may affect the tyre's aspect ratio and thus diameter. The key measurement is the overall diameter.

Q5: How much difference is significant?
A: A 3% or greater difference may require speedometer recalibration to maintain accuracy.