SLS AMG Roadster: “Stable even without gullwings”

Merc’s gullwinged SLS AMG has already launched to rave reviews and filled up order books around the globe, and now the stage is set for the open-topped version to keep the impetus going.

Pictured alongside is the SLS AMG Roadster, which is currently undergoing final testing, with the company’s engineers said to have devoted particular attention to bodyshell rigidity, driving dynamics and NVH.

The Roadster was developed by AMG in parallel to the Coupe, and test mules have been trundled out with little more than adhesive foil over the badges (although why even the latter was necessary is open to debate).

As you can glean from the accompanying images, the ragtop carries over the long-snout/short-tail proportions of its coupe sibling, and the fabric roof appears nicely integrated with the windscreen frame and bootlid.

That said, we’ll reserve final judgement until we’ve seen it in the metal (and cloth) on September 13 at the Frankfurt motor show.

AMG development director Tobias Moers emphasises the need for chassis stiffness, saying: “Without bodyshell rigidity there are no handling dynamics, and neither can the close fit of the soft top be guaranteed.”

As the Roadster variant was already on the agenda during the conceptual phase for the SLS AMG, the lightweight and rigid aluminium spaceframe was specified at a correspondingly early stage, says Moers.

According to Mercedes, the lack of a fixed roof and gullwing doors made it necessary to design more robust side skirts, not just for crash performance, but because test drives showed that the driving dynamics could be improved even further by strengthening this area.

In addition, the cross-member that supports the dashboard has additional struts at the windshield frame and at the centre tunnel, while a structure between the soft-top and fuel tank allegedly stiffens the rear axle.

Mercedes claims these features prevent unwanted vibrations and eliminate the need for “additional weight-increasing vibration dampers often employed by competitors”.

Despite its added stiffening measures, the bodyshell of the Roadster tips the scales at only 244kg – barely more than the 241kg of the SLS AMG Coupe’s bodyshell.

Merc claims the three-layer soft-top can be raised or lowered in 11sec at speeds of up to 50km/h, and it’s stored behind the seats in a Z-formation to save space. The fabric roof is claimed to provide a low centre of gravity, and the SLS AMG Roadster has a quoted v-max of 320km/h (electronically limited).

Mercedes claims the roof (whether open or closed) generates no “flapping, booming, hissing, clattering, whistling or howling”, even at top speed. The refinement is attributed in part to the seamless, bonded-in rear window made of single-layer safety glass.

Read the latest Carsales Network news and reviews on your mobile, iPhone or PDA at carsales' mobile site...