Quote...." however from my understanding the difference between the 8 and 9 inch Fuchs is all on the inside depth not the outer depth...."
That's incorrect also....
See this posting ---> my post # 4 within--->
http://forums.pelicanparts.com/porsche-911-technical-forum/290040-anyone-have-928-21mm-spacers-911-a.html There, I say ( by verifying records)-->
"... Basically, a 911 8" Fuchs places all of its extra 1" width ( compared to a 7" Fuchs) toward the outside of the car, relative to the original mounting hub. Therefore , when I added a 21mm spacer with my 7" Fuchs.... it was just shy of the 1" ( 25.4mm) extra width that a 8" Fuchs ( w/o spacer) would have done for me. It means I could have gone another 4 mm to "exactly" place the outside edge of the rim like a 8" Fuchs would .
However, you're starting off with a 8" Fuchs. By comparison, a 9" Fuchs ( w/o spacer on the original mounting hub) would place * it's * extra 1" of width the following way...
an extra 10 mm toward the outside...and an extra 15mm toward the inside. Not all 25 mm is toward the outside !..."