Three things to consider.
1) Off road. 8's will air down further and stay on the rim better. I run 6 to 8 psi on 35x12.5 BFG AT's on the trail (8" wheels). A little mud, dirt, sticks and rocks works their way in between the tire and rim, but seldom blow a bead completely. I would give the 8's a grade of 95 and the 10's down in the 60's or 70's for staying on the rim, maybe even a little lower than that. Also the bulge created by the 8's tend to protect the rim a bit more, but the truth is that when you drop the psi real low, the sidewalls move sideways pretty easy and protection for the rim is just marginally better. I run cheap steel wheels and replace them one at a time when necessary - usually 2 or 3 a year.
2) Highway. 8's bulge out more and thus cause the tread to be more rounded instead of flat on the pavement. Grades: 8's maybe an 80 and the 10's in the 90's for flatness of tread on the pavement and maybe a little bit more stability because you can air the 10's up a little bit more and still have a flatter tread line.
3) Looks. Totally opinion, but the 10's look much better unless bulgey, donuty looking tires and wheels are your thing.
As far as I am concerned am much more concerned about off road usefullness, the highway manners are close enough to not matter that much, and I couldn't care less about how it looks, so I run 8" wheels.
Doug '97 TJ
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