Most tire manufactuer's websites have a max wheel width they recommend putting a specific size tire on.
Keep in mind, just because a tire will go on a rim, does not mean it is getting its full effective contact patch. For example, you can waste the money on a 235 or something, but since the wheel is more narrow, it will actually pull the sidewall in, which A. has a poor effect on cornering stability, and B. reduces your contact patch to not much more than a 215 anyways.
Now, that was for the sake of example
. I have no experience putting tires on the stock 3.7 rims, i am merely trying to make a point: Bigger is not always better.
Another important thing to remember is tire height. Assuming you go with a size different than stock (and you are not tuned), you will need to get something the same size as stock to not effect your Speedo and/or shift schedule if you're an auto.