Originally Posted by
dddd
Those narrow, raised areas that run out to the rim sidewalls are the bead seat shoulders.
The shoulders are supposed to be of a very precise [nominal] diameter...
FIFY 
Just a minor nitpick on your always excellent technical insights... allowing for the possibility of an out-of-round wheel, the measured diameter could vary somewhat from the precisely specified nominal, but hopefully the
circumference at least, is both precise and invariant (temperature and hoop stress being held constant
.