[vujade]

almost any diameter rim should fit under a beetle fender and still be able to turn.
remember that a stock tire (165 sr 15) has a diameter of 25.5"

as you increase the size of your rim, you can decrease the size (aspect ratio) of your tire and this should accomodate the increased rim size.

For example:
205/60/15 = 24.7" diameter
205/50/16 = 24.1" diameter
204/40/17 = 23.5" diameter
215/35/18 = 23.9" diameter
225/35/19 = 25.2" diameter

So you see, any of these tires can be fitted under a beetle's fenders. Alot has to do with how low you make the car and how wide your wheels are & what offset they have.