Tyre Size & Diameter Calculator

How the Calculator Works

We break each tyre size into three parts: the tread width in millimeters, the sidewall height as a percentage of that width (aspect ratio), and the wheel diameter in inches. From there we calculate the total tyre diameter and how much it will change.

• Overall diameter: Sidewall height on both sides plus the wheel diameter (converting inches to millimeters).
• Ride height change: Half of the diameter change, since only the radius affects ground clearance.
• Speedometer error: A larger tyre makes the speedometer read slightly slow; a smaller tyre makes it read slightly fast.

Tips for Picking the Right Size

1. Stay close to stock diameter: Aim to keep total diameter within 2-3% to avoid big speedometer errors or clearance issues.
2. Check clearance: Wider or taller tyres can rub on fenders, liners, or suspension components.
3. Match load and speed ratings: Ensure the new tyre meets or exceeds the vehicle's requirements.
4. Recheck pressure: Verify recommended pressures after changing sizes for the best wear and ride quality.