Detroit motor show 2012: All-new Mercedes SL

Mercedes boss Dieter Zetsche has set his company the target of being the world's largest premium car maker by the end of the decade on the eve of the Detroit motor show.

Mercedes currently trails class leader BMW in global sales, and Zetsche believes taking leadership of the premium sector, which is expected to grow at an even faster rate than the entire new car market, is key to success.

"This year is impossible to predict, nobody can be certain what will happen," said Zetsche. "But we are very confident that the next decade will see significant growth for the whole car market, and the premium sector in particular. We want to be number one in that time."

Zetche said his confidence was down to the new products being developed by Mercedes, including the new Mercedes SL, which is being shown in the metal for the first time at the Detroit motor show and will deliver “the ultimate in passionate, refined motoring” when it arrives in UK showrooms next July according to its makers. The new roadster will go on sale in the UK almost 60 years to the day since the original 300SL became the first German sports car to win the Le Mans 24Hrs.

The sixth-generation SL is based on an all-new platform, but apart from that it diverts from the proven recipe of the outgoing model only among the details.

As is the class norm, and like the R230 model, the new R231 SL uses longitudinal V6 and V8 petrol engines and rear-wheel drive. But unlike many direct competitors, it has a folding metal ‘vario-roof’ that takes less than 20 seconds to convert, and a strictly two-seat cabin.

Featuring cleaner surfaces and bolder styling lines than the outgoing car — none more so than the unbroken shoulderline running from headlight to tail-lamp — the new SL’s aesthetic references are to the 1960s ‘pagoda’ SL and 1970s R107. However, Mercedes hasn’t wasted the chance to update the car with the SLS-inspired upright radiator grille used by its sports car family, and some familiar body-side sculpting.

The exterior form is functional as well as elegant. Mercedes claims the SL is the most aerodynamically efficient car in its class and sets new standards for wind noise-based cabin refinement.

But the car’s biggest technological advancement is under the skin. This SL will be the first Mercedes in large-scale series production to use an almost exclusively aluminium construction.

Made from a mix of chill cast, vacuum die cast, stamped and extruded aluminium, this body-in-white superstructure allows the new SL to be between 125kg and 140kg lighter than the outgoing steel car, and 20 per cent more torsionally rigid.

The metal castings and tailored blanks of the SL’s body-in-white are connected via various techniques, depending on how much load they transmit. While some parts of the underbody are MIG welded, hemmed, bonded and bolted together, others are joined via state-of-the-art friction stir welding — a technique that allows for particularly stiff, precise joins.