Backspace help

Going to run a 38 or 40" tire on my JL while my axles are being built. In the meantime does anyone know first hand what offset will allow my tire to clear at full lock? Will have narrow bumpers front and rear. If I have to go with a 3.5" backspace I will but would rather have them tucked in more if possible. Wheel suggestions for stock axles? Or is anyone has a used set I'm open as well.

Does not need to be a beadlock either for the short term. Going with TR beadlocks in a 5.5BS for the axle swap.

If you have a Rubicon, your factory axles will be almost full width and you can get away with a lot more back spacing. But, I assume you have a Sport or Sahara being that you're doing an axle swap and so, you'll really want to run wheels with less back spacing. Assuming you'll be running 13.50 wide tires, I'm gonna bet that you'll want at least 4" of back spacing to prevent rubbing at a full lock and even at that, you may find it necessary to adjust your steer stops.