Strictly speaking you have 2-piece rims, that is it takes 2 pieces to make a complete wheel: The wheel weldment and a single locking ring which form the outer wheel "rim" or lip. I know most automotive tire shops will not work on them but most truck and tractor tire places will. Just recently I replaced the old tires, tubes and flaps (liners) from 3 of my wheels for my 50 3/4 ton myself. I went to a local Rural King store and bought a "rim" tool. Those locking rings have a notch that the tool is made to go into. It's hard work with lots of prying and hammering, and you'll need another tire tool, or two. Mine were rusted bad. That ring has an inner edge or lip that goes into the wheel gutter, or groove. Part of that inner edge is left off on purpose. It tapers down to nothing about 2" long 2 places 180 degrees apart. The tool notch is 3-4" away from one of those tapers. You insert the tool in the notch and pry the ring up until the tapered places clear the wheel....I could see that back when those wheels were new and didn't have 50 years of rust on them that job was not too bad.
Disclaimer: Always be careful when prying or hammering on rims or wheels - You could get hurt.
Good luck.
