Tire Size Calculator







Understanding Tire Size Calculation

The tire size calculation involves determining the sidewall height, tire diameter, circumference, and number of revolutions per mile based on the tire's width, aspect ratio, and wheel diameter.

Formulas Used

Sidewall Height:

\[ \text{sidewall height} = \frac{\text{profile ratio} \times \text{width}}{100} \]

Tire Diameter:

\[ \text{tire diameter} = \text{wheel diameter} + (2 \times \text{sidewall height}) \]

Circumference:

\[ \text{circumference} = \pi \times \text{diameter} \]

Revolutions per Mile:

\[ \text{revolutions number} = \frac{63360}{\text{circumference}} \]

Calculation Example

For a tire with code P215/65R15:

Width: 215 mm, Aspect Ratio: 65%, Wheel Diameter: 15 inches

Sidewall Height:

\[ \text{sidewall height} = \frac{65 \times 215}{100} = 139.75 \, \text{mm} \]

Converted to inches:

\[ \frac{139.75}{25.4} \approx 5.5 \, \text{inches} \]

Tire Diameter:

\[ \text{tire diameter} = 15 + (2 \times 5.5) = 26 \, \text{inches} \]

Circumference:

\[ \text{circumference} = \pi \times 26 \approx 81.7 \, \text{inches} \]

Revolutions per Mile:

\[ \frac{63360}{81.7} \approx 776 \]