About Tire Size Calculator
Tire Size Calculator compares two metric tire specifications and shows how changing tire dimensions affects overall diameter, circumference, revolutions and indicated speed.
Inputs are processed locally in your browser and are not sent to Navorika.
How the calculation works
Sidewall height
Sidewall height = tire width × aspect ratio ÷ 100.
Overall diameter
Overall diameter = rim diameter converted to millimetres + two sidewalls.
Speed difference
Estimated actual speed = indicated speed × new tire diameter ÷ original tire diameter.
How to use this calculator
- 1Enter the original tire width, aspect ratio and rim diameter.
- 2Enter the proposed replacement tire size.
- 3Enter an indicated speed for the speedometer comparison.
- 4Review diameter, circumference, revolutions, clearance and estimated actual speed.
Understanding the result
A larger overall diameter travels farther per wheel revolution, while a smaller diameter travels less distance per revolution.
Clearance change represents half of the overall diameter difference.
Important limitations
- This calculator compares nominal tire dimensions only and does not establish safe vehicle fitment.
- Actual mounted dimensions vary by tire model, wheel width, pressure, load and manufacturer tolerances.
- Verify wheel width, offset, load rating, speed rating and vehicle manufacturer requirements.
Frequently asked questions
How is tire diameter calculated?
Two sidewall heights are added to the wheel or rim diameter after converting the rim diameter from inches to millimetres.
Why does tire size affect speedometer readings?
Changing tire circumference changes the distance travelled per wheel revolution.
Does a similar diameter guarantee fitment?
No. Width, wheel offset, suspension clearance, steering clearance and ratings must also be checked.