Originally Posted by racer_d

It all comes down to wheel offset. The 265-35-18 was the factory size rear tire when Boxsters were ordered with 18" rims (admittedly, on 9" wide for boxsters), so I wouldn't worry about the tire.. I would worry about the rim.

The suggestion above (xusmnj....)my post is a great idea. Be sure to put a towel/cloth on your jack so you don't scratch your rim either.

My guess is that, with the car merely raised, the clerance is tighter than when the car is lowered, due to the movement of the rear suspension.