Okay, I went and did it. 255/40s up front and 275/40s out back on the stock 17 inch rims. Like one of you said, above, there is more sidewall bulge with the 275s on the stock 17" rims, but it doesn't look that bad to me at all---maybe it's the sidewall design of these tires that minimizes it? They're Falken ziex ZE 326s, probably not up to a lot of the tires seen on this forum, but the price was right and they got a high speed rating, VR or maybe ZR, dunno for sure, will have to look. They are a good looking performance tire, and look a lot like the ones on SnakeCharmer's convert. in profile and design. I'm a little disappointed in that the 255/40s up front increased the wheel well gap somewhat from the 245/45s, but the big 275s in the rear fill it up good. Seems like the car has a bit more quickness on initial acceleration, maybe due to the the wider rubber in the back, or is that just my imagination and wishful thinking?? Overall, I'm real happy with the ride and improved handling.