It depends on your front end type, transaxle type, shock absorbers, and weight distribution. I have the big tank, full sized spare in the trunk, IRS transaxle, and a ball-joint front end with Bilstein shocks - IM installed an adjustable 19mm tubular sway bar made for a Porsche 911. The bar is currently set at "medium" tension and works very well for my driving style. Remember that VS, JPS, CMC, and Fiberfab cars have more rear weight bias (engine/transaxle in my IM is about 2 3/4" farther forward) so you might want to try a bar in the neighborhood of 15mm or 16mm (stiffness goes up as the square of the diameter?). Read Greg Ward's article on VW handling (swing-axle and IRS) at www.callook.com.