This has always been the dream of driving a convertible, a light roof in summer and solid roof in winter. For a long time there was only the 'hardtop', this had to be stored when not in use or be mounted when required. If only all this could be done by pressing a button, one could exploit every ray of sun with an open roof or drive well protected, fast and streamlined on the highway with the top closed. This is especially important for Germany, the biggest buyers of convertibles, although not always with the best weather.
The further development of hydraulics makes it possible. Just a half a litre of hydraulic oil in a system with a hydraulic pump (figure 2), up to 180 bar pressure, ultra-thin piping and work-cylinders (figure 3). However, one should begin with the complicated lever-rod assembly. One system swings both roof parts out of the boot, the other enables the opening of the boot lid in two different directions. Each is moved by a slender working cylinder on either side. Another hydraulic cylinder is responsible for the double locking mechanism in the folding roof front edge. Nowadays, the folding is even possible when driving slowly.
In the event of a system failure, either two people are necessary to solve the problem by releasing the systems using brute-strength, or an expert who can operate the system manually. Damage is very likely however, if the single necessary steps are carried out in the wrong order. At which point we come to the disadvantages. How usable the remaining boot space is when the folded roof is in place, can be seen in figure 1. A rear impact has always been more expensive with the convertible, with these contents in the boot, the expense becomes almost prohibitive.
The more serious argument actually is, that convertible roofs are only possible since the windscreen, for aerodynamic reasons, slopes very far towards the rear. If the windscreen also has a wide upper edge, the feeling of open driving is slightly diminished. Should the locking mechanism in the roof require also a few centimetres, driving with open roof benefits at most those in the rear seats, who have however, very little seat comfort. 09/08