[NewArt]

I have a set of wheels, originally from a C4, that I bought last fall. I mounted them on my 2001 S Boxster and they fit, albeit with a wider stance. Here's the specs:
rear: 10j x 18 ET 40 , with 265/40/18
front: 8j x 18 ET 54 , with 235/40/18

Originals are:
9j X 18 ET52, with 265/35/18
7.5j X 18 ET50, with 225/40/18

So, as I see it, this is the equivalent of running spacers of about 10 or 12 mm rear and 2 to 4 mm front, taking into consideration the difference in the rim width.
I know that this is a lot of numbers, but I've seen that some of you are quite clever with these sort of calculations.

Question 1: They didn't cause problems (rubbing) with the Michelin Sport Alpin winter tires, but do you think they could cause me grief at the track with Michelin Pilot Sport PS2 ? (I'm still in Green run group).

Question 2: Any disadvantages to this setup, either to the car or to the handling?

Thanks for your input! -James