I had some MT 29.5X9X15's on my car and had problems with the diameter being too big. They where rubbing the some screw heads that hold the splash shields wheel wells. These screws where at the bottom rear of the well opening. When I had a pair of MT 28X9X15's on the car there was tons of room it seamed. They are actually closer to 27" diameter than 28. I dont have a summit catalog handy but look up the diameter and section widths of the two tires recommended and look up the same specs of the tires you are talking about and see how they compare. From my experience it seams like a section width of a little over 11" and dia of around 28" is about as big as will go.
