This is one of those cases where the OP's location might be useful. I don't know if he lives in a tropical swamp, or maybe in the NW where it rains for 8 months, then is dry for 4, etc.
Bruce
Maybe. But if it ain’t fit to drive on, it ain’t.
Liquid in rear tires plant rear tires better (traction), but it is not ballast, ballast hangs off rear of tractor and use weigh to cantilever weight off front making front end lighter.... Its the old playground teeter totter syndrome...
Dale
Have you looked at 11L-15 tires or other tires that are used on most hay balers or for floatation. Also, since it is 2wd you could put pretty much any tire that would fit on the front even if it is one size bigger or smaller without throwing the center of gravity of too much. If you go with 16 rims it would shift the center of gravity more toward the rear of the tractor to give more traction but the 3 point hitch would lose an inch or lift. If you find the right bolt pattern and offset on the rim, you can also use wide 15 truck tires. I have used them on hay trailers and that has help keep them from sinking into the mud a lot.