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Retractable hardtops becoming more popular as costs drop, reliability increases
WIM OUDE WEERNINK | Automotive News Europe
Posted Date: 8/19/05
French automaker PSA/Peugeot-Citroen SA has turned the retractable hardtop convertible into a mainstream car with the help of the Peugeot 206 CC.

Since the 206 CC was introduced in 2000, Peugeot has sold 325,000 units of the coupe-cabriolet, which has a retractable hardtop from French coachbuilder Heuliez.

That's fitting because Peugeot pioneered the retractable hardtop in 1934 but sold only a few dozen. In 1957, Ford Motor Co. introduced a two-piece folding hardtop convertible in the United States called the Skyliner. It sold 50,000 over three years.

But a series of drawbacks -- including cost, storage space, reliability and durability -- kept automakers from using folding hardtops for decades.

The idea resurfaced in the mid-1990s on the Mercedes-Benz SLK, which was co-developed by Mercedes-Benz and German coachbuilder Karmann AG. But folding hardtops at first were limited to premium cars that could stand the system's higher manufacturing costs.

Then the Peugeot 206 CC arrived, proving people would buy mass-market hardtop convertibles. The 206 CC's success forced European volume-brand automakers to consider hardtop convertible variants for nearly every small and medium-sized platform they develop.

The players

The field is full of coachbuilders and convertible-top specialists offering retractable hardtops. And they are developing new technology to broaden the appeal and capabilities of convertible hardtops.

Germany's Car Top Systems, a wholly owned subsidiary of Porsche, is the largest supplier of retractable hardtops. Car Top Systems supplies roof systems to the Mercedes-Benz SLK and SL and Peugeot 307 CC.

Car Top Systems' two main rivals are Heuliez and Karmann. But competition is building: Webasto subsidiary Open Air Systems -- Oasys for short -- and Edscha AG are becoming formidable hardtop players with new designs and technologies.

Since Mercedes' and Peugeot's hardtop debuted, companies have used much the same approach and have applied it to relatively small cars.

Those hardtops are two-piece roofs that fold into a clamshell shape -- the rounded exterior on the outside and interior sections inside -- and stow in the trunk with the help of electric motors.

Better technology

All competitors have addressed the quality and reliability issues of hardtops and have tackled other technical problems.

"We have developed a second-generation sensor switch that not only has an on-off mode but also can detect the top's position during the open-close operation," Heuliez CEO Paul Queveau says. "It has made the top faster and more reliable."

The system also automatically lowers the side windows whenever operating the top and raises them after the top is up.

"That improves water and air management because the windows (fit) better into the rubber seals," Queveau says.

When automakers remove fixed roofs from unibody structures -- which are designed so that every portion of the body is a structural member -- the car flexes more. With soft-top convertibles, the top is also flexible and will work even if the body is only lightly modified to make it more rigid.

Hardtop convertibles require more rigidity so the metal top's panels will fit. But the requirement is not a hardship for automakers because some degree of stiffness provides a sensation of high vehicle quality, says Thomas Schuett, managing director of Webasto subsidiary Open Air Systems.

"The market requires more stiffness for better comfort anyway, both with the roof stowed in the luggage compartment or with the roof up," he says.

Special care

Retractable hardtops typically are subsystems that are assembled at a supplier's plant and shipped to assembly lines. But fitting a roof system to a car requires special attention because body structures tend to bend when they are shifted from the assembly line conveyor belt onto their wheels.

Heuliez considered this in developing its production process for the two-seat Opel Tigra TwinTop.

"For better fit and to reduce adjustments once the roof system has been fitted to the car, we mount the module when the car is on its wheels, not on the conveyor belt," Queveau says.

But this assembly procedure is not exclusive to Heuliez. Karmann, the hardtop system supplier for the Nissan Micra C+C, does it the same way.

Karmann has set up a roof system production line for the Micra C+C inside Nissan's assembly plant in Sunderland, England.

Most other retractable hardtop suppliers either make their coupe-cabriolet models in their own factories or have plants near their customers.

Car Top Systems has a hardtop plant in Bremen, Germany, for the Mercedes SL and SLK, as well as a factory about 50 miles from Peugeot's plant in Sochaux, France, where the 307 CC is made.

Webasto is building a factory in a supplier park near Volkswagen's Autoeuropa assembly plant in Setubal, Portugal, that will supply the folding glass hardtop system for the Volkswagen Concept C.

VW will start production of the four-seat cabriolet in 2006.

Karmann ships retractable hardtop systems for the Renault Megane coupe-cabriolet from Germany to France.

For cost reasons, most hardtops are made of high-tensile steel. Usually, only premium models use aluminum or composite materials, which weigh less. One exception: Oasys uses aluminum for the Daihatsu Copen coupe convertible from Japan.

source:http://www.autoweek.com/news.cms?newsId=102995