We had this same problem with our 1997 2188. It started with lug bolts braking off. We must have went through bucket fulls of them. They replaced them with upgraded ones. They still broke. Then we found the first set of cracked wheels a couple of years after we bought it. Case replaced them, and within a year they were cracked. During this time we also blew out a tire at the bead. The tire guy said they had too much weight on them. Here is what the dealer and I found out.....
All the machines that we found that cracked the wheels seemed to have these things in common.
!. Aftermarket larger bin extensions
2. 38" rims
3. Large heads 30' platform, 8 row cornhead etc.
Also our 2188 had a downhill stance toward the front. All the 21/2388s with 42" wheels set level, and didn't have a problem cracking wheels. Also the combine was very nose heavy. Even after we filled the rear tires with water & calcium it was still nose heavy. I told the dealer that it was because all the weight from the big heads and large extensions were putting too much weight on the front end. If we put 42" rims on it to level it out it would distribute the weight more evenly, and put less stress on the front end. Thus ending the problem. Finally Case agreed if I paid the difference between 38" and 42" rims. So we agreed and put 42" rims and new heavier 18.4R42 tires. We also installed the new lugs with the reinforcement bars. After doing this the combine set level, and wasn't nose heavy anymore.
In the end we ran it for 3-4 years with no more problems. Hope this helps.
Just to back up what Big A said; in the manual for our 2052 (973) header it says not to use a 36' on 18.4R38 duals. I think they were just talking about weight capacity on the tires, but I can see how lots of weight can effect the rims too. We've got 42" duals on our 2388 and haven't had any problems with the rims. The tires themselves are in pretty poor shape, though.