I have a 96 bronco w/ 6" suspension lift and a 3" bodylift I have 33x12.50s on stock rims now. I want to put 38x14.50's. I have minor tire rub now(at full turn) how much backspacing would be required to fit bigger tires?

 

If you move the tires outward by changing the backspacing, they'll steer in a BIGGER arc, causing MORE interference with the body at the front & back corners of the wheelwells. Rubbing the radius arms or sway bar won't hurt the tires at all.