Originally Posted by Volk Z

I would recommend if you are going 18 inch then
18x9.5+22
18x10.5+12
A quick lesson- if you stay with those widths then if the number goes up then it will actually sink in more or end up closer to the hub. Lower number would yield pushing it out or "poking" the rim/tire
Tire size you can go
255-40-18 front 305-35-18 rear
Or 265-40-18 and 285-40-18 rear
You can mix and match above as they would both fit on the rim sizes above adhering to the lower tire size for the 9.5 and the 285 or 305 for the rear rim.