The super beetles have a design issue with the strut suspension. I was told that the front of the car does not have enough weight for a strut suspension. When a number of the components in the front end get worn the car will develop a "shimmy" or "shake" between 40 and 55 mph. Put 100 lbs of weight in the trunk to see if it is eliminated or reduced. See that attached link.
http://www.toplineparts.com/frameset.htmlDoug