Originally Posted by Charley3
8 to 9
Good luck finding a 9" rim.
If you plan on sticking to 10.5” tires 7" or 8" rims are both good choices. An 8" rim will encourage a flatter tread contact patch and more even wear.
If you plan on going to 12.5" tires in the future consider 8", but know that a 12.5" tire will also wear better on a 10" wide wheel for the same reason described above.
If you plan on wheeling and airing down your tires, it is advantageous to run the narrower wheel as it will hold a bead better. You will need to run a little less PSI to prevent crowning of the tire which will wear the middle of the tread faster than the shoulders.
FWIW, I run 12.5" tires on 10" wide wheels and air down to 10-12 PSI when on the trail and have never popped a bead despite putting plenty of sideload on the tires. Most 3 ply MT type tires are stiff enough to resist splitting the bead for even aggressive wheeling.