To measure the wheel circumference, you can proceed in this way:
- place the bike in an open space
- Apply tape in a straight line
- position the bike on the tape to let the bike remains always on the line
- just rotate the wheel until the valve for inflation is at the lowest point
- mark in the tape with a pen the point where the valve coincides
- move the bike along the line created by the scotch until the valve back into position for the third time ( make 3 full turns of the wheel on the floor )
- mark in the tape where again the inflation valve is located at the lowest point
- measure the distance between the two points scored in scotch
- divide by 3, to calculate the actual circumference of the wheel ( having made 3 full turns of the wheel and then dividing the value by 3 helps to minimize the measurement error )