Will 18x9 fit on the front?

[Kroggers]

OK, so the car is now in the body shop getting the scars from the 2012 season removed, and the front and rear fenders getting widened. I will get an extra 1.5" - 2" on the front and an extra 2" - 2.5" on the rear. This I hope will give me more options on wheel size etc.

I run with Michelin Pilot Sport Cup, and looking at available size to fit a 18" wheel I am considering going for 295/30 - 18 at the rear and 265/35 - 18 on the front.

Initial thought is to get a 18x10 wheel on the front and an 18x12 on the rear, and this leaves me with a question - what offset do I require to make the wheels fit the Boxster?