How big can i go ?
 

I have a 98 f150 4x4 with stock suspension. I have already put some 18" wheels from a lightning on it with 265 65 18 tires. I came across a deal on some brand new 295 70 18 mud terrains. My question is will they fit by leveling the truck with the torsion bars or do i need to go with a smaller tire ?? Thanks.

I could be wrong on this, but I'm pretty sure the lightning wheels had a higher backspacing than the other oem wheels (somewhere around 5.5" versus 4.5" on the other 97-03 oem wheels).

If this is true, I think you'll have some rubbing issues with a tire that wide being tucked into the wheel well so far. If possible, I'd try to test fit them before purchasing.

I agree. I can't remember the specs on the Lightning wheels but they are different. I'd test fit one first, but I think you are gonna have to stick with a 33 inch tire.