OK you fitment experts. I think i know the answer but will defer to the group this time!

I know my stock hollow twists are 18x8 ET 50, and 18x11 ET 45. Although not part of the question, I also happen to run 7mm spacers in front, and 18mm in rear. Look perfect to me.
That takes me to 43 front and 27 rear if my math is right.

So here is the Q:
Im looking at a set of used wheels/tires "listed" as direct fitment for 996tt.
Will these fit on a standard 996 turbo suspension (ie large factory spring perches etc):
9 x 18, ET 57 front. NOTE wheel is wider than stock by one inch, on 245's
And
11 x 18, ET 39 rear on 295's (stock width)

They seem so close, but I got "burned" on a set earlier this year, that supposedly were the right fitment, but i was wrong. I was able to sell them luckily. I can adjust out with spacers if needed, just want to ensure I'm not rubbing on the inside or similar.

Thanks and happy holidays all.

 

So you are at 18 x 8 et43 front, 18 x 11 et27 right now,
New wheels are 18 x 9 et57 and 18 x 11 et39.
1 inch is 25.4mm, so it's equal to 18 x 8 et31.6 for the front,
So the front will stick out about 11.4mm more than the current setup.
The rear is less aggressive, so you can fit 12mm spacer to have the current fitment.

You can measure your clearance between the edge of the lip and the fender and see if you have the space to fit.

In my opinion, you can be more "flush" with the new wheels, with no spacer in the front, and 18mm spacers in the back. (11.4mm stick out in front, 6mm stick out in rear).

You are going away front the suspension/brake so you don't need to worry about the back spacing.

Good luck.