I have '86 euro 930 and offset phone dials (7JR16, 8JR16).
Could you please tell me how thick of a spacer in the rear should be? I want them snug in the fender well.
Thanks in advance!

 

Depends on the offset of your PDs and your particular chassis. Not all chassis' are created equal.

What does this mean? Do you want the rims pulled in toward the body or pushed out toward the fender lips?

If the PDs are 23.3 mm, you could probably run a 60-65 mm adaptor in the rear to push the 8" rims out toward the fender lips and run a 20-25 mm spacer in the front, adding longer wheel studs to the hubs. Depending on your chassis/alignment, you might even get away with moving the rear 28 mm spacer to the front, though, this could be a little too snug.

 

mel_t_vin

I want the rims pushed out toward the fender lips.
Thank you

 

Okay, then my recommendations stand.

The 8" et 23 PDs will sit ~20 mm in-board of the stock 9" et 15 Fuchs [minus 12 mm in width and minus 8 mm in offset]. The stock setup with the 9" Fuchs has at least half an inch [12 mm] of clearance toward the rim lip. So, take the stock spacer of 28 mm, add 12 mm for rim width, 8 mm for offset, and another 12 mm for that "flush fender" look, and you get 60 mm.

Rim fitment is part art and part science. We just discussed part of the science [numbers]. Unfortunately, no two chassis are exactly the same. Even the same chassis can be different, left to right. A 60 mm adaptor should be safe but could potentially leave you 10-15 mm more room, per side, to the rim lip.

See if you can find someone with a spare set of 60-70 mm adaptors laying around collecting dust...