When you don't know how to measure the wheel correctly is when.
Lay a tape measure across the face of any wheel and it'll measure about 1" bigger than the tire it takes. The wheel has that lip to retain the tire side wall for a reason.
A = Where the tire actually mounts and that's 15" in this scenario
B = The face of the wheel and that measures 16" in this scenario
C = The lip that retains the tire to the wheel via the tire pressure
point taken, never really thought about where you would actually measure a wheel. the way it was worded before made it sound like that was just how things work, like a 2x4 is actually about 1 3/4x3 3/4, but in reality, if you measure where the tire sits it is 15 inches, you just cant cause of the bead lip