I have 9.5 inch wide rims in the back, I suspect that 10 inch wide would not be a problem, but after that you are going to start getting VERY close to things.

Check the inside clearance on the stock rims and you can figure out how much wider to the inside you can go without hitting anything.

CAUTION: If your tires are wide and the rims are close to the inside you will probably run into the tire rubbing problem I had before I put 4mm spacers on the back. The upper inside of the wheel well was being rubbed by the tire at full articulation. (when I say inside, I mean inboard of the wheel)

Hope that helps. Good luck!