When creating a convertible from an existing coupe, the Body-In-White structure loses up to 85% of its torsional and beaming stiffness when the fixed steel roof is removed. The convertible engineer must regain this lost stiffness by strategically reinforcing the underbody structure. Due to total vehicle mass limitations however, ride quality is often sacrificed as a direct result of the mass required for the convertible top framework, or “topstack”.Traditionally, steel stampings and aluminum diecastings have been used for the topstack structure. Magnesium, in the form of high pressure diecastings and extrusions, is uniquely qualified as a topstack material. The primary benefit of light weight is less effort required to operate the convertible top. The secondary benefit of this lighter weight allows a greater percentage of the vehicle mass to go toward more structural reinforcement of the body, improving the ride quality of the vehicle.