Tire Size Comparison Calculator
Compare two tire sizes to see diameter difference, speedometer error, and ride height change.
Enter old and new tire sizes in standard format.
Tire Comparison Results
Tire size format is read as: Width/AspectRatio RimDiameter (e.g., 225/45 R17).
Overall Diameter Formula:
Diameter = (2 × Sidewall Height) + Rim Diameter
Sidewall Height = Width (mm) × (Aspect Ratio / 100)
Then convert to inches: Diameter (in) = (2 × Sidewall in mm) / 25.4 + Rim (in)
Speedometer Error:
Actual Speed = Indicated Speed × (New Diameter / Old Diameter)
If the new tire is larger, your speedometer reads slower than actual speed. If smaller, it reads faster.
General guidelines:
- Stay within 3% of original diameter for safety
- Larger tires improve ground clearance but may rub fenders
- Smaller tires reduce ground clearance but can improve acceleration