Estimated actual speed only. This tool does not recalibrate vehicle electronics. Speedometer behaviour varies by vehicle.
How tire size changes indicated speed
A larger rolling diameter travels farther per wheel revolution, while a smaller diameter travels less. This calculator compares the theoretical diameters of the original and replacement tire sizes.
Formula: estimated actual speed = indicated speed × new tire diameter ÷ original tire diameter.
Important limitations
Real tire diameter changes with brand, model, pressure, load and wear. Vehicle electronics may also apply their own correction. Use this as a planning estimate, not as a calibrated speed measurement.