I have thought to buy that bigger spacesaver sparetire, lots of them available.
With 3,5 x 17 rim, i should not worry with 310mm brakes at front. Tire is skinny 105/90 R17, alternative size is 125/80 R17
Should fit great to under balljoint beetle hood =)
Now i am thinking to sell the existing 15" spacesaver rim:
