The absolute "largest" tire that will fit on the stock OEM 18x7 rim is LT285/75R18 (35" O.D.). This extremely tall and wide tire will require "lifting" the VX. There are only three(3) tires made in the world in this specific size. They are:
A: TOYO - Open Country A/T (All-Terrain type)
B: TOYO - Open Country M/T (Mud-Terrain type)
C: MAXXIS - "Bighorn" M/T (Mud-Terrain type)
On a "non-lifted" VX, the largest tire that will fit on the stock OEM 18x7 rim is LT285/65R18 (32.4" O.D.). See the photo gallery of "LITTLE LAURIE" with BFG A/T's in this particular size. Most owners of "non-lifted" stock VX's put on one of two(2) different sizes:
A: LT285/60R18 (31.4" O.D.)
B: LT275/65R18 (32" O.D.)