[PaulE]

The stock sizes for Boxster 17 inch wheels and tires were 7 inch width, ET 55 offset front and 8.5 inch width, ET 50 rear. The OEM tire sizes were 205/50 x17 front and 255/40 x 17. The stock 18 inch wheels and tires were 7.5 inch width, ET 50 offset front and 9.0 inch width, ET 52 offset rear. The OEM tire sizes were 225/40 x18 front and 265/35 x 18. Your all season setup sounds like it would be better used for the winter tires. The staggered 7/9 17 inch setup you're looking at sounds like they are from a 996. If the offsets are the same as the stock 17 fronts and 18 rears they will work, and they may still work if the offsets are close but need some spacers. If the wheels you're looking at buying are OEM, the widths and offsets should be cast into the rims on either side of the valve stem holes.