It is not so bad. For the older tractors, like my
B8200, only two tire types were offered, turf or ag. Both sets of tires required specific rims. If you had Ag's, and wanted turfs, you had to buy tires and rims, and vica versa. The tire sizes and rim diameters are different, but the rolling diameters were the same to keep the proper ratio. When I started the switch to R4, I had to research tire sizes to insure the R4 had the same rolling diameter and ratio as the specced Ag and turf.
Now, you can get R1/Ag, R3/turf, and R4's. All the tires differ in size, but the rolling diameter stay the same(or very close as to not make a difference) for a particular tractor(at least 4x4 tractor)
The Ag's and R4's tend to use the same back rim, and tend to be the same size specification. Ag's though, tend to use a narrower rim. Turfs use different, wider rims, although sometimes the same front rim works with the R4, which tends to be a wide tire.
So... For the most part, if you have turfs and want to switch to Ag's, you need rims too. If you want to switch to R4, you will need new rear rims, and maybe new front rims.
If you have R4's and want to switch to Ags, the back rim should work, but a narrower front rim is typically needed. If you want to switch to turfs, you need new tires and rims.
If you have Ag's , and want to switch to R4, you'll need a wider front rim. If you want turfs, you need tires and rims.
In the event that tires wear out, and you stay with the same tire type, then replacement should be simple.