Yes.
I have had a set of Cayenne 18" 8 x 57 wheels in my junk pile for a year and last week my wife said that she wanted them on her car. I said, "No, they won't fit." I rolled a wheel over to her Boxster with a big Cayenne tire on it and showed her that it was way too big for the wheel well.
"No" was an easy answer, but I kept thinking about it. She is tired of the 20s and wanted a change. I realized that I have an old set of 18" tires that I could mount on the Cayenne wheels just to check it out - no money lost buying a set of new tires just to experiment.
Today I took two of the wheels along with a front and rear tire to have them mounted. I had the stock sizes figuring that even though the wheels are 'square', having a slightly undersized tire in front and oversized tire in back would still balance out to similar diameters (both just under 25") and an asymmetric footprint.
The sidewall on the fronts rises straight up from the edge of the wheel. The rears push out slightly beyond the wheel, but not to an extreme. The fit is actually much better than the 20s (which were always at the extreme edge of 'fitting'). I have a small spacer on the rears, 5mm I think, and no adjustment in the front. Plenty of clearance all around.
Now that I know they work, I'm going to get some new tires and do both sides. This car is not tracked or driven particularly hard. The choice is purely for how my wife wants her car to look.
