Wheel expertise wanted!

[E30King]

So I've got my eye on some new wheels for my E30 'vert. I'm looking into getting a set of 16x7 Rota RBs. I know that the centre bore for an E30 is 57.1mm (which is available) and the original offset is 25. Now the ones that are available, is as follows..

16x7 (4x100/ET40/57.1) The issue I have is with the offset, I do believe with an offset of 40, the rim would be in more, rather than stick out. So there will be the possible issue of rubbing the struts etc. What would the ideal spacer size needed, to be able to clear inside the fender, and not rub the fender line? Would I need to roll my rear fenders in?

There is however, the same rim, in other variations with offset. I know there's ET0, and I think ET 28, I'm not too sure. But the site that I'm looking for just shows ET40 with a 4x100 pattern. So I'll have to ask if they can get them. Going to ask if they can get 16x8 as well.

Input on this topic would be appreciated!

[Shifty_k]

wheel offset is measured in mm, so et0 would be the mounting face for the wheel is in the center of the rim. Et 40 would mean the mounting face of the wheel is 40mm out from center thus moving the wheel in.Et 0 would look cool, usually the less offset the more dish and aggressive look! google offset, there are a few calculators online to figure this stuff out.

[DesktopDave]

There's a big thread over on R3v about this.  If I find it I'll post it.  +1 on Shifty's suggestion:
http://www.1010tires.com/wheeloffsetcalculator.asp

Are you 100% sure on that offset?  My stock 6j14 bottlecaps are et35.  If my math is correct, half the rim width + offset (- spacer) = inner overhang.  Three inches is about 75mm, plus the 35mm offset = 110mm overhang, or about 4 1/2".

Given that "safe margin," 110mm, you'll get a different value for each width.  To maintain that figure, rims would require the following offsets:

A 7" rim would have maybe 24mm offset, and stick out 26mm, another inch
8" with 12mm offset, 50mm more outboard (two more inches here)
9" at zero offset would stick out 3" further
10" is crazy talk and you shouldn't think about it.

I've had 8x16's on my car and would not advise it.  The tires needed to be 235/40 R16, they made the ride very harsh, rubbed the front wheel wells and didn't wear very well.  Many sizes will need spacers.  If you decide to go that route, make sure they're high-grade metal and hub-centric.  I'd suggest a max of 15mm thick spacers with extended lug bolts, install racing studs if you need more space.

Personally, the biggest I'd go is a 15" rim.  IMHO they just look "right."