Tire Size Calculator
Calculate tire dimensions, compare sizes, and check speedometer accuracy
Primary Tire Size
Tire Size Results
Formulas used: Sidewall Height = (Profile Ratio × Width) ÷ 100; Tire Diameter = Wheel Diameter + (2 × Sidewall Height); Circumference = π × Tire Diameter
Important: Tire diameter changes should not exceed ±2.5% for optimal compatibility
Understanding Tire Codes
Width
The tire width in millimeters from sidewall to sidewall
Profile Ratio
The sidewall height as a percentage of the tire width
Construction
R = Radial, D = Diagonal bias, B = Bias belt
Wheel Diameter
The diameter of the wheel rim in inches
How Tire Size is Calculated
Sidewall Height: (Profile Ratio × Width) ÷ 100
Tire Diameter: Wheel Diameter + (2 × Sidewall Height in inches)
Circumference: π × Tire Diameter
Revolutions/Mile: 63,360 ÷ Circumference
Important Notes
- Tire diameter changes should not exceed ±2.5% for optimal compatibility
- Larger tires may cause clearance issues or affect vehicle performance
- Smaller tires may reduce ground clearance and affect handling
- Always consult a professional when changing tire sizes
Example Calculation
Standard Car Tire
Tire Code: 215/65R15
Width: 215 mm
Profile Ratio: 65%
Construction: Radial (R)
Wheel Diameter: 15 inches
Calculated Results
Sidewall Height: 139.8 mm (5.5 in)
Tire Diameter: 26.0 in
Circumference: 81.7 in
Revolutions/Mile: 776
Tire Tips
Check tire size compatibility within ±2.5%
Larger tires may affect speedometer accuracy
Consider clearance issues with bigger tires
Consult a professional for major size changes