Here are the specs on the stock 19" wheels, which is identical to the 17" wheels in everything except diameter.
19" x 7.0 "
offset = 50mm
bolt pattern = 5 x 114.3mm (5 x 4.5 is equivalent)
hub bore = 67.1 mm
The tires on the GT are Toyo A23, sized 225/55-R19, selling at tirerack.com for $265 each as a "Grand Touring All Season.
You can go to one of two "plus-zero'" sizes on your 7"rims, according to tirerack: 235/50-R19 or 245/50-R19. You might be able to go even wider to 255/50-R19, but you may start to run into rubbing issues.
The second plus-zero option has a nice sweet spot option: the Pirelli P-Zero Nero All Season, sized 245-50-R19, is only $179 each and ranks #6 on the survey of UHPAS (Ultra-High Performance All Season tires. If I was going to replace the OEM tire in the first year on 19"rims, this is what I would choose.
HOWEVER! The Toyos we have are not too bad, at least by OEM standards. They should last at least 18-20k miles. As you've noticed, not too many tire companies are making in our size (yet). If you wait a year you might be able to get the Continental ExtremeContact DWS in a size to fit your stock rims.
ANOTHER REASON TO WAIT is that once you change the rubber, you've forfeited a certain amount of your warranty protection, regarding handling, road noise, etc. If you think these could be issues, keep the OEM rubber and let your dealer deal with it.
And of course, the 3rd reason to wait is to save $800-1200, for the rubber, balancing and mounting.
FIRST POST!!! Picked up a 2014 GT on Tuesday. Traded my 2009 370Z, which will be sorely missed.
