European roof suppliers are developing a second generation of retractable hardtops large enough for big convertibles and let passengers have better views even when the top is closed.
Some of these tops -- all being developed independently by supplier specialists located in Germany and France -- will replace painted metal panels with glass.
Other new-generation retractable hardtops contain three or more metal panels that can span greater distances. That extra reach allows automakers to build convertibles with true four-seat capacity instead of cramped 2+2 configurations that offer virtually no leg room for rear-seat passengers.
Karmann created a glass roof for the Renault Megane CC and for the new Nissan Micra C+C as well. The glass panels are bonded in steel frames similar to the way windshields are constructed.
"It adds light and creates a fresh-air environment for the small coupe interiors," said Christian Rennert, Karmann's account manager for international markets.
Automakers want to construct bigger hardtop convertibles to meet consumer demand for more space and utility. For this, those first-generation two-piece folding hardtops just won't work.
"Their clamshell geometry takes a lot of luggage space and cannot cover large body openings," said Thomas Schütt, managing director of Webasto's roof system subsidiary Oasys. "So windshield angles have to be more acute than on regular cars and the design proportions are a bit odd, with long rear overhangs and high luggage compartments."
The Renault Megane CC and Peugeot 307 CC are typical examples of first-generation solutions, offering just 2+2 interior space with a two-piece clamshell hardtop. Passengers must bend to enter and exit because of the cars' low rooflines and sharply angled windshields.
But next-generation retractable hardtops will abandon the one-fold, clamshell approach entirely.
Among the solutions: multiple-section roofs that stack, or nest, atop each other so the roof can be stowed more compactly.
This autumn General Motors Europe will be the first with a five-piece hardtop. It will debut on the Opel/Vauxhall Astra TwinTop.
|German supplier Edscha has developed a three-panel retractable hardtop. It combines a glass rear windshield with two painted-metal roof panels into a sedan-like package. When lowering (second from top), the glass stows separately and the roof panels stack (middle image) before all panels are stored in the trunk (bottom image).|
In 2000, Opel first showed a similar roof that it had developed with CTS in the G100 design study.
And in 2001, Karmann presented its own solution: a three-piece roof.
"You have more freedom to fold it, in a Z-shape or otherwise," Rennert said.
Webasto's Schütt compares multiple roof-section folding to the layers of an onion. The end result is better packaging.
"It takes up to 40 percent less space in the luggage compartment," Schütt said.
Because new multiple-section retractable hardtops span greater distances, designers can retain the standard car model's windshield and reduce development costs.
Said Schütt: "Multiple-section retractable hardtops offer more design freedom, including a higher greenhouse. They also create real four-seat interior space, with the looks of a traditional softtop."
On the downside, multipiece hardtops are: more expensive to manufacture; add design complexity; and require the use of more engineering resources.
Because the metal panels cover greater spans, assembly must be more precise.
"You need more stiffness in the system and more fixation points," Schütt said. "And gap tolerances between roof pieces as well as rubber seals are more crucial."
Cooperation between carmakers and roof-system suppliers is important since retractable hardtops are such specific technology, automakers say.
"You need mutual understanding for design as well as engineering requirements," GM Europe's Leopold said. "We chose to work with the oldest suppliers of retractable hardtops, CTS, when developing the Astra TwinTop."
Fold or stack?
How clamshell and multipiece retractable hardtops compare
Two-piece clamshell roof
Multiple-piece stacking roof
Retractable hardtop makers and their customers
Cadillac XLR, 2 seat
Mercedes SL, 2 seat
Mercedes SLK, 2 seat
Peugeot 307 CC, 4 seat
Opel/Vauxhall Astra TwinTop, 4 seat (late 2005)
Renault Megane CC, 4 seat
Nissan Micra C+C, 4 seat (September)
Pontiac G6, 4 seat (2006)
Peugeot 206 CC, 4 seat
Opel Tigra TwinTop, 2 seat (complete car assembly)
Daihatsu Copen, 2 seat
Volkswagen cabrio, 4 seat (2006)
Volvo C70, 4 seat (late 2005)*
Ford Focus, 4 seat (2006)*
Mitsubishi Colt, 4 seat (2006)*
Alfa Romeo Spider, 2 seat (2006)*
Ferrari Maranello Super America, 2 seat
BMW 3 series, 4 seat (2006)
Peugeot 207 CC, 4 seat (2007)