required backspacing for 35's

[pieterb]

I am looking at getting a ReadyLift Kit 3.0"F/2.0R put on our 2007 Expedition XLT so I can put on 35's. My questions is what kind of backspacing will I need. Is there a easy way to calculate depending on rim/tire size? I was hoping to stick with a 17 or 18 inch rim and then put on offroad tires.

Edit: I guess I am trying to figure out what my offset should be on the new rims to keep the tires from rubbing on anything.

Any help/info would be greatly appreciated.

 

[Hamburgertime]

Did quite a bit of trimming to get 315/70/17s on my 17x9 -12mm offset (believe that is 4.5 inches of backspacing) have seen some other members do that. Have an 08 myself with the 3/2 readylift. 35s will be bigger than my tires. I don't think I'd be able to get away with any more backspacing personally. My tires measure in at about 33.75" tall at 35psi.

Edit: My backspacing makes my tires stick out quite a bit from the fenders... may need to buy some flares if I get caught .