SAN DIEGO – General Motors set out to create a “coupe-like” ride in the new ’11 Chevrolet Camaro convertible, using BMW 3-Series and Ford Mustang drop-tops as measuring sticks to gauge their accomplishments, chief engineer Al Oppenheiser says.

During a recent test drive here, Oppenheiser tells Ward’s a major priority was eliminating “cowl shake,” a term used to describe body flex in convertibles created by the loss of rigidity that comes with a hard top.

The goal was made easier because the Camaro program was developed with a convertible model in mind, he says. However, GM’s bankruptcy in 2009 put the vehicle in limbo.

“A lot of programs were put on hold while we reassessed our resource issues and which brands would survive,” Oppenheiser says. “The convertible was considered a product that was going to win in the marketplace. We just had to wait our turn.”

To optimize the convertible’s stiffness, four body reinforcements were added to the Camaro frame. They included a tower-to-tower brace under the hood, a transmission support reinforcement brace, underbody tunnel brace and front and rear underbody “V” braces.

The improvements provided torsional rigidity of 18 Hz and a 21-Hz bending rating, numbers that are “fantastic for a convertible,” Oppenheiser says, noting static stiffness was “actually stronger than a BMW 3-Series,” something he says was confirmed by a third-party test.

It also bests the Mustang by “approximately 2 Hz in both global torsion and global bending,” he says. “And those chassis changes don’t compromise the sporty ride we wanted that you would normally find in a coupe.”

Another problem that threatened the convertible program was the unexpected loss of a key supplier.

“While we were asleep, Edscha (Cabrio Dachsysteme), our top supplier, went bankrupt,” Oppenheiser says. “We had to resource the (cloth) top to Magna CTS (Fahrzeug-Dachsysteme).”

Finding a new top supplier was difficult because Chevy and Edscha engineers had worked collaboratively designing the convertible roof system so it would integrate flawlessly with the Camaro body.

“We had a 3-armed system and a Z-folding top, whereas Magna had a 2-armed system,” Oppenheiser says.

“We had to work with them because we couldn’t compromise any of our bodywork for wider openings, as the dies were already out being tooled. So they had to package their 2-arm system for the opening we already had designed into the sheet metal.”

Extra measures are taken to make sure the soft tops don’t leak, starting with an 8-minute water test at GM’s Bowling Green, KY, plant, where the Corvette convertible is built.

The tops then are shipped to Oshawa, ON, Canada, where the Camaro is assembled, and installed before undergoing a second water test.

Wind noise was an important issue, as well, and Oppenheiser says the Camaro’s 3-ply top with a sound deadening headliner is nearly as quiet as the coupe and surpasses the Mustang.

He also points out that while folding hardtops generally are more quiet than their canvas counterparts, they are too pricey and sacrifice too much trunk space. Heritage also was a factor.

Says Oppenheiser: “Our decision from day one was always to do a soft top to stay true to the tradition of Camaro, which never had a hardtop convertible.”

bpope@wardsauto.com