A 2x8 is actually only a 1.5"X7.5". I made mine out of 2x10's and part of me wishes I have made them a little wider. You are running 8.5" wide rear wheels with stockers and most tires stick out a little past the wheel. So a 7.5" wide base for close to a 9" wide tire is a little small. It's still fine as long as they are positioned right, but better safe than sorry.