We priced some 480x50's about the early farm shows time frame.   Wanted Firestones. Quotes were 8500-9000.00 for 4. Found a dealer in Dyersburg Tn who had some on Ebay. Paid 6000.00 delivered. We mounted them ourselves this spring. Pulled them off the tractor. Used the skiddy to break the beads loose. Plenty of lube and a couple of truck irons to get the first bead off, flipped the tire over, hooked the rim to the forklift and lifted the rim out of the second bead. Lubed the bead and the edge of the rim. Basically rolled the tire up to the rim in the floor and slammed it down on the rim. The first bead would slide right on. Lubed the second bead and took the tire tools and put that side on. Put a couple of blocks under the center of the rim, just enough to lift the rim up to seal the bottom bead. We took the valve stem adaptor off and screwed a Milton male fitting with a 1/4" female thread. We then hooked the 1" hose from our 185 CFM IR  compressor and let it go. In a minute or two with that volume of air it sealed right up.