Originally Posted by AntiPrius
A 31" (31x10.5x15) is the biggest you can go with no lift, and no other alterations such as cutting sheet metal. With a simple budget boost, you may get 32's on it.
I don't think this is what the OP is asking,
I believe he's asking if he can put a 12.5" wide tire on a 8" wide rim, or something along these lines as to the widest tire he can put on a stock rim.
Now, don't forget that if you use stock rims with oversize tires, you will need spacers. that's why most change wheels to get different backspacing.
edit: just re-read OPs post, AntiPirus, he is asking more than 1 questions. Your answer was good.