The "XX.5" rims will all be for tubeless tires, and will be 1-piece construction. For instance, a 16.5" rim will have the same profile height as a 15" tube type rim, the 17.5 will interchange height-wise with a 16" tube tire, etc. Trying to use a 17.5 tire on a 17" split rim is deadly dangerous- - - -the bead shape is different and the tire will blow off the rim, even if a tube is used to trap the air. One of my friends nearly lost a hand when he tried to install a 15" truck tire and tube on a 14.5" mobile home rim. The bead wires of the tire broke on the tapered rim seating area as the pressure came up, and the tire blew off the rim.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!