Hey stud, having doubts about the rims? Backspacing is a measure of the distance from the inner edge of the rim to the inside mounting surface. Thus, the larger the backspacing number, the more your wheels (and tires, obviously) "tuck" under the vehicle. The smaller the backspacing, the more the wheels stick out. Spacers effectively decrease your backspacing. So, with the backspacing you're looking at, you'd be more likely to rub your tires on the outer lip of your flares. If this happens, there are several fixes....longer bumpstops to limit upward travel, a small body limit to give you more room to flex, installing those shackles you've probably still got sitting behind your back seat
, or wheels with more backspacing. To go back and answer your original question, spacers are needed when using wheels with large backspacing (like 5.5" on the TJ Canyons and Gamblers) to prevent the inside of the tire from rubbing. Hope that helps. If not, I'm sure you'll let me know.