This form will help you correctly configure the tire diameter to enter in VESC Tool. A simple measurement isn’t enough; several factors need to be considered:
1 - Rider weight (just like battery range, rider weight has an impact and should be taken into account).
2 - Tire compression under load.
3 - Manufacturer’s recommended pressure.
4 - Your usual riding pressure.
I hope this tool helps you, and your speed should match reality.
Example for a 76kg Rider (167.5 lbs)
The tool is here:
https://onewheelworldmap.ct.ws/calc/calcdiamtire_us.php
(Translate into German, Italian, Brazilian (Portuguese), Spanish, French).