The man at OK Tire tells me mounting a 225 or 235 (75-15) on my stock 5.5" wide wheel is no problem. He said that although manufacturers dont recommend it (and he's not giving his personal guarantee that it wont pop the bead) the fellow says mounting and running that size tire on that size rim is no big deal. He said popping the bead is not the issue, rather, the bulging out of the sidewall is the issue. He recommended airing down to make sure the entire tread is in contact with mother earth.
Fellow also said that once the tire and rim have had time to get to know each other, the tire gets a little grove in it, kinda helping to keep the bead in place. Hope he's right.