I, too, today went to the dark side with a Yokohama ADVAN Neova 175/55/16. .... Can't wait to get it mounted and try it out.
A 175/55-16 tire has a diameter of about 23.6", almost 2" smaller than the stock setup!!!
The tire is also very expensive.
What lead you to decide to buy this particular tire and size?
I'd be interested to hear back regarding you experiences with this tire.