Not to burst your bubble(s) but....

I don't believe you can get an 18" wheel/tire combo to be the same O.D. as stock. Definately not the 19"s. I think you are looking at least 1/2" taller min.

Do you guys understand exactly how the Synergy drive works? It's a pretty intense control system.

I would be very, very, very cautious about going to larger O.D. tires, my gut feeling is you will send the control system into a wild freakin frenzy, but I could be wrong...