Re: My new ford fouces.
True^, I just met with a 2012 owner not too long ago, and recently she was asking about putting 18 inch wheels on it, and it was strongly suggested that she sticks with the 17's. You go with a bigger rim, and the tire must be skinnier, therefore, more easily popped on pot holes.
Trust I had 205/40/R17's, and I popped one on a small pot hole, now I have 205/45/R17's, and they are much more comfortable, especially with a lowered car. We have even been talking about picking up some 16 inch rims, for winter, and Auto-X racing, but it also means I'll be able to bump the tire size to 205/50/R16, which will make the ride much more quieter, and smoother.
And, as far as lowering it, you can, their are plenty of kits out there for it, but as R.S said, you might void the warranty on certain things.