right now I have weld drag lites on it, the front is fine but the rear ones rub the outside wheel well. I rolled the finder and it still rubs over bumps. the tires are 235/60/15 bfg drag radials. The rims have 3 1/2" backspacing. I want to put a 265/50 on it so should I go with a 4 1/2 or 5 1/2 backspacing?