AUBURN HILLS – Chrysler Group reveals its entry in the growing retractable hardtop market with the ’08 Chrysler Sebring, but the long and the short of the story is proportion, its designer says.

The auto maker takes the wraps off the car at the L.A. auto show, but the development process saw its dimensions waver during the age-old tug-of-war between form and function.

A key goal was to design the convertible’s trunk to accommodate a folded roof and two golf bags – without compromising the sleek profile it inherited from the Sebring sedan, Joe Dehner tells Ward’s during a sneak preview here at Chrysler headquarters.

The convertible’s original design featured a roof that was 4 ins. (10 cm) shorter, from A-pillar to C-pillar, than the final version, Dehner says. But the car’s overall length was the same as the sedan – 190.6 ins. (484.2 cm).

Those proportions made the roof appear “stubby,” Dehner recalls.

Then designers added 4 ins. (10 cm) to the car’s length, as well as its roof.

“It looked like hell, so we backed (the overall length) off to 3 (ins. [7.6 cm]),” Dehner says.

The end result is a car that is 193.8 ins (492 cm) in length with a 108.9-in. (276.6 cm) wheelbase that is 2.9 ins. (7.4 cm) longer than the model it replaces, which also is America’s best-selling convertible.

Combined with a 61.9-in. (157.2 cm) track, the Sebring convertible – which is all-new aft of the A-pillar – features expanded crush space in the engine compartment and boasts superior handling and ride comfort.

Chrysler’s performance goal was to create “a solid feel with no cowl shake, whether the top is up or down,” says Larry Lyons, vice president, front-wheel-drive product team.

To this end, Chrysler reprises a strategy of material selection that debuted on the Dodge Caliber C-car, whose platform is closely related to the one that supports the D-segment Sebring. Both cars make liberal use of roll-formed, high-strength steel, but high-strength steel tubes in the Sebring’s sill structure and dual-phase steel in its rear rails contribute to a body that offers nearly 2.5 times more torsional stiffness and is 1.5 times more resistant to bending.

The car also features a windscreen, but it can only be used when the 4-seater’s rear positions are empty. Nevertheless, it enhances the top-down experience, Chrysler says.

“We extensively tested the convertible and the windscreen in our Auburn Hills aeroacoustic wind tunnel and achieved some very dramatic results,” said Dennis Krozek, chief engineer-Chrysler Sebring Convertible. “With both the top and the windows down, the windscreen reduces buffeting and wind noise by approximately 11 to 12 decibels. With the top down but the windows up, the windscreen reduces buffeting and wind noise by about 5 decibels.”

Scheduled for a first-quarter production launch when it will join the Sebring sedan at Chrysler’s assembly plant in Sterling Heights, MI, the new model is the first convertible to offer three roof choices: cloth, vinyl and a retractable hardtop. Each uses the same mechanism, which deploys the roof in less than 30 seconds.

Supplied by Wilhelm Karmann GmbH, it is triggered by a one-touch button.

With the retractable hardtop, the Sebring enters a market already populated by the Pontiac G6, Volvo C70 and Volkswagen Eos. The G6 and Eos are new models for their respective brands, but Ward’s data show the C70, which replaced a soft-top Volvo, has delivered to the Swedish auto maker an incremental U.S. sales gain of 2.2% through October.

The Sebring is America’s top-selling convertible marque. Since 2001, Chrysler says it has averaged annual sales of about 150,000 units per year.

The auto maker expects buyers will be split evenly between men and women. The average buyer is between 40 and 50 years old, married, well-educated desires open-air freedom without sacrificing the practicality afforded by a comfortable every-day vehicle.

emayne@wardsauto.com