Highlights Of The New 911 Carrera 4/Carrera 4S | Part Six

Porsche 911

Porsche 911

Aerodynamically styled roof

The roof of the open-air Carrera 4 and Carrera 4S comes in the same proven shape and technology as the roof on the Carrera Cabriolets with conventional drive. The roof opens and closes fully automatically at the touch of a button, folding into the roof compartment in Z-configuration, with the outer side of the roof facing up when open to protect the heated rear window made of glass. The entire roof mechanism can be operated at a speed of up to 50 km/h or 31 mph, the roof opening or closing together with the windows in a mere 20 seconds.

One of the particular fortes of the soft roof on the Porsche 911 is its outstanding aerodynamic quality. While the tissue structure of the soft roof has a slight influence on the car’s drag coefficient, the actual measurements are exactly the same as on the Coupé: As a result, both Carrera 4 Cabriolets pass the wind tunnel test with a drag coefficient (Cd) of 0.30 (Carrera 4) and, respectively, 0.29 (Carrera 4S).

To use the flow of air rushing past the car for optimum downforces, the spoiler moves up 20 millimetres or almost 0.8 inches higher than on the fixed roof Carrera. This it does automatically at a speed of 120 km/h or 75 mph. And since aerodynamic forces are less significant at low speeds, the spoiler moves down again once the speed of the car drops below 80 km/h or 50 mph.

Low centre of gravity thanks to the soft roof

The outer skin of the roof is made of top-quality textile tissue protected inter alia from UV light in order to avoid even the slightest bleaching effect. The front section of the roof between the windscreen and the first tightening bracket running parallel to the B-pillars is tightened by a light but stable cast magnesium panel. A plastic panel fitted between the outer fabric and the inner roof lining, in turn, serves not only to hold the roof fabric in place, but also to keep out noise and ensure adequate thermal protection.

The roof structure is made up of 10 major components, with a share of 26 per cent aluminium and 20 per cent magnesium. The other materials featured in the roof include steel forgings, the fabric and textile itself, the intermediate roof layer, the roof liner, and various seals.

Including the hydraulic opening and closing system at the rear, the soft roof weighs just 42 kg or 93 lb overall. As a result, the soft roof on Porsche’s Carrera Cabriolets weighs only half as much as a comparable retractable steel roof, with a correspondingly positive effect on the car’s driving characteristics: The less weight there is in the upper section of a car, the lower the centre of gravity. And this, obviously, is essential for a sports car with a high standard of lateral dynamic performance.

Hardtop as an option

Weighing only 33 kilos or 73 lb thanks to its aluminium structure, the hardtop comes as an option. Porsche is thus accommodating the wishes of many customers who prefer to drive their Carrera Cabriolets with a soft roof also in winter - especially as the car has all the qualities for leaving on the soft top during the cold season.

To optimise soundproofing, the hardtop is now fastened at the rear by two bolted connections, and no longer by bayonet catches. Fitting the hardtop in position is very easy thanks to its low weight, as on the previous model: All you do is place the hardtop on the car, the two connections points at the rear automatically establishing an electrical connection for the rear window heating, without requiring any additional cables. And like the soft roof, the hardtop now comes with new seals for perfect drainage of rainwater.

continues... | Part Seven
Published 22 July 2005 Melanie Carter

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