Originally Posted by
pismocycleguy
Where does the size designation come from for 20 inch wheels? Where do you measure to obtain the 20 inch size measurement? Is it the rim size, the tire size, or the outside diameter of the tire when mounted on the wheel? I need some clarification!
Thanks,
PCG
The 20" size designation must come from the marketing department.
Nominal tire sizes in inches seem to be closest to the ouside diameter but this varies with the tire you fit and the actual sizes are sometimes so far off that even this can't explain it.
The metric sizes seem to be more meaningful. I assume that they are the diameter in mm of the rim surface on which the tire bead is intended to sit. This would be a bit smaller than the outer diameter of the rim.
David