1989 S4 wheel types, etc.

This is a snip from a post made by Kim Crumb, a 928 expert, many years ago.  It addresses your question about changing wheels on the 928:

Wheels from other Porsche models (nearly invariably) don't fit the front of 928's. The standard factory offset was 65 mm (front) through the entire 17+ year production run. We have more a more advanced a-arm suspension...other Porsche models use "strut" front suspension, and those late model ones have tended to have offsets in the 52-55 mm range. Pushing the wheel OUT a half inch, when, if anything, it would be better to go IN! When I put a 55 mm offset 8.5 x 17 wheel on the PROJECT 928 car (way back in the summer '90) the 235 tire rubbed on the fender lip. And you could get your fist between the spring and the wheel.

Does that "fit" make any sense to you? It didn't to me. I drove down to OZ/MSW (650 miles) the very next day to show them, after my complaints seem to have limited impact. Ultimately we tried an experiment...we added an inch to the inner rim half (three piece wheels) and voila, no rubbing.  A 9.5 x 17 68 mm offset wheel made it work (the tread area "recenters" itself back that critical half inch.) One of the many technical 928 breakthroughs provided in that intense 12 month development effort. The data is there, even if it isn't "convenient" some times. My later story on "Wheels and Tires" in the December '97 Panorama only re-emphasized the measurements, on 18's. When I published the PROJECT 928 series in PANORAMA in the summer of '91, some wheel companies complained. One even tried to have me removed as the 928 PCA Tech Advisor. If you can't win on the facts, try to win with intimidation... THEN the factory came out with their special wheels for the 928 GT Cup (for the German Porsche Club) and guess what front wheel they had? A 9.5 x 17, 68 mm offset, wheel...EXACTLY as I had said. I would think that would have ended the discussion about "what works"...the factory has clearly verified that as the best spec. Later I went to the big SEMA show, to hand out those factory specs. Hoping that more 928 wheels would get then created.  Mostly the opposite happened, people were often rude... same reaction, they didn't like this news. In my world, you'd want to know the facts!   Obviously they want to keep selling 944 & 911 wheels to 928 owners, despite the facts. Oh, too bad that 9.5 x 17, 68 mm offset, factory wheel was so expensive and heavy (27 lb, cast wheel...from the rear of the 911 Carrera Cup racecar) so it isn't much of an answer for us, except to verify the fitment parameters. Hey, I don't like this any better than anyone else, because it means (at least so far) that expensive wheels are what it takes to really fit up a 928, as designed...and I also know that having a "dislike" reaction doesn't change the facts, either.
Kim