Got my answer direct from the dealer's service people. They are quite sure they can flash the correct code into the computer to make up for the tire dia difference. Now the big question is can I afford the classy wheels.I guess I asked this question on the wrong topic board, here's a copy:
Wheel & Tire Question:
If you want to trade in your 17" set up and put on full size 18" wheels and tires can the dealer's service people readjust the computer to keep the numbers right?
I wouldn't want to get larger wheels and thin tires that don't fill up the wells.