Guys have fit up to 4.75" backspace before with no rubbing, the width of the tire is really what determines if it will rub or not. BUT with 8" wide wheels it'll have a wimpy stance with that much backspace because the wheels will be far inside the wheel well. With an 8" you can go with a 3.5" or 3" backspacing to bring more of the wheel to the outside of the car and make it look more aggressive.