you can go 1.5" but most are just 1". I'm running 1" SpiderTrax spacers on my XL-7 with 265/70/16's, which is a 31" tire. I ran 1.5" spacers on my GV with 245/75/16's. Both will still rub somewhere, but of course not as much as they do now. the 1.5" spacers get the tire far enough from the frame to where is whouldn't but there any more, but you might catch your firewall because of the increased swing circumference of your tire.