For a 7.5" wheel 215 is your MINIMUM and I'd think that 225 or even 235 would be better for tucking the lip in a little. I hate when the wheel is wider than the tire...looks retarded.
Things to keep in mind are the rolling diameter, whether it's gonna tuck under the fender, and whether it's gonna rub on the splash shields.
At 225 your tires are wider than the wheels so the wheel width becomes irrelevant. All that matters at that point is the tire size and the wheel offset which determines the location of the center of the tire relative to the hub. Figure out the offset of the wheel before you proceed.
From personal experience I can say that a 225 tire with 40 offset tucks nicely under the fender (though not by much) but that it also rubs (just barely) on the inboard splash shield. I also get rubbing on the forward splash shield but that's because of my tein caster bushings which place the wheel about 1/2" forward in the well. 235 and 245 add just a little under a half an inch each to the total width of the wheel. You could probably run a 235 tire at 40 offset but at 245 I'd think you'd need more like 45 offset to keep it under the fender so you'll want to check that.
To keep it at under 25" rolling diameter (but over 24.2" which is stock) your options are 225/35/18 (24.2"), 235/35/18 (24.5"), 245/35/18 (24.75"), and 225/40/18 (25.08"). For comparison my setup that I was commenting on is 225/50/16 (24.9") so neither of your 0.35 series options is likely to rub the front splash shield the way mine does. Both of them will likely rub a bit on the inboard splash shield if you turn hard...but who cares?
Moral is... I recommend either the 225/40/18 which will give you little to no inboard/outboard clearance issues but may rub the front splash-shield, or 235/35/18 which will be a little smaller, a little wider, and probably still give you no rubbing issues. But make sure you know the offset of those wheels.
