Tire Size Calculator
Calculate tire dimensions, convert sizes, and compare tires
Your Input
Select a calculation type (dimensions, convert, compare, or speedometer), enter tire size(s), then click Calculate to see the result and step-by-step solution.
Complete User Guide
What is Tire Size?
Tire size is a standardized way of describing tire dimensions, including width, aspect ratio, and rim diameter. It affects vehicle performance, speedometer accuracy, and handling.
How to Use
- Select calculation type
- Enter tire size(s) and options
- Click Calculate to see the result and step-by-step solution
- Use Reset to clear and hide results
Tire Size Formats
Metric (P-Metric):
205/55R16
205 = Width (mm)
55 = Aspect Ratio (%)
16 = Rim Diameter (inches)
Imperial (Flotation):
31x10.5R15
31 = Overall Diameter (inches)
10.5 = Width (inches)
15 = Rim Diameter (inches)
Tire Dimensions
Width: Tire width in millimeters or inches
Aspect Ratio: Sidewall height as percentage of width
Rim Diameter: Wheel diameter in inches
Overall Diameter: Total tire diameter including sidewalls
Circumference: Distance around the tire
Formulas
Sidewall Height:
Sidewall = (Width × Aspect Ratio / 100) / 25.4
Overall Diameter:
Diameter = Rim + (2 × Sidewall)
Circumference:
Circumference = π × Diameter
Revolutions per Mile:
Rev/Mile = 63360 / Circumference
Speedometer Difference
When you change tire size, the speedometer reading may become inaccurate. Larger tires make the speedometer read slower, while smaller tires make it read faster.
Formula:
Actual Speed = Indicated × (New Diameter / Original Diameter)
Important Notes
- Tire size affects speedometer accuracy
- Larger tires increase ground clearance
- Wider tires improve traction but may rub
- Check vehicle manufacturer recommendations
- Consider load rating and speed rating
- Aspect ratio affects ride comfort
Common Applications
- Tire replacement planning
- Wheel and tire upgrades
- Speedometer calibration
- Tire size comparison
- Vehicle modification