I think about 10 gallons per tire. So it depends on what you fill it with. WW fluid is ~8# per gallon, so that would add 80#. Rimguard or calcium is ~11# per gallon, so would add 110# to the empty tire weight. Which I would guess to be maybe 40#
If you fill the rear tires of a kubota BX2370 with R4's, how much will the tires both weigh after filled with ballast?