New 2021 Mercedes-Benz SL: bespoke shell shown ahead of reveal

All-new, aluminium-intensive body shell is stiffer than both previous SL and current AMG GT

Mercedes-AMG has revealed new details of the composite aluminium body shell used by the all-new SL roadster, due later this year.

Completely unrelated to the structures that underpin the previous-generation SL and current AMG GT, the new body combines an aluminium space frame with a "self-supporting structure".

Mercedes claims the development process was particularly challenging given this new SL features a 2+2 seating arrangement, and will accommodate a wider variety of powertrain options. The priorities, it says, were to "present the driving performance characteristic of the brand with a focus on lateral and longitudinal dynamics, as well as to meet the high expectations in terms of comfort and safety".

A combination of aluminium, steel, magnesium and fibre composites was selected for the best balance of lightness and rigidity, with the new SL boasting an 18% increase in stiffness over the old model. Transverse rigidity, AMG claims, is up 50% over the AMG GT Roadster, while longitudinal rigidity has been boosted by 40%. 

The main body shell - without the doors, bonnet, boot lid and other exterior fixings - weighs 270kg.

Recently, the firm released images of the upcoming SL roadster undergoing winter testing, ahead of its official reveal in summer.

The reborn convertible will square off against the Porsche 911 Cabriolet with a range of hybridised straight-six and V8 engine options.

The images showed multiple SL variants side-by-side in minimal disguise, highlighting two different fabric roof options. This confirms Autocar’s previous reports that the SL will arrive with a traditional fabric hood in place of the folding hard-top arrangement that has been used for the past two incarnations.

Mercedes also confirmed that the 2+2-seat SL will be sold under the AMG brand only and will be offered with fully variable 4Matic+ all-wheel drive. While much of the SL's development was handled virtually, final on-road testing will soon include the north loop of the Nürburgring, hinting at the car's sporting ambition.

Previous spy images gave clues as to how different model variants will be told apart: prototypes with circular exhaust outlets are believed to be an entry-level hybrid variant - likely the SL 450 EQ Boost - while ones seen with more aggressive-looking pipes and raised rear spoiler are expected to be the top-rung SL 63 AMG. 

The prototypes bear a strong resemblance to that which featured in official images released by Mercedes last year. The SL shows a clear family resemblance to the Mercedes-AMG GT, with a rounded rear end, long bonnet and a pair of slim horizontal rear light clusters.

The SL is set to be revived as a lighter, faster and more engaging model partly inspired by the brand’s motorsport roots, which is why overall development duties have been assigned to the AMG performance division. It will be the first time AMG has overseen development of any SL across its previous seven generations.

Last year, then-AMG boss Tobias Moers confirmed that the SL will be “aligned” with the next AMG GT. The duo's shared aluminium-intensive platform, known as the Modular Sports Architecture (MSA), will increase the economies of scale and overall profitability of two of Mercedes’ most exclusive model lines.

“We’re bringing back the historic DNA of the SL," he said. "It's far sportier [this time round]. It will have a perfect compromise between driving dynamics and comfort, because it’s still kind of a cruiser, too.”

He also confirmed that the eighth-generation SL will be offered only as a roadster, like its predecessor. It is expected to go on sale in the UK towards the end of 2021.

*SL and GT sharing*

As well as sharing a common platform structure, the two upmarket Mercedes sports cars are expected to share axle assemblies, suspension, steering systems, 48V electric architecture and hybrid drivetrains, among other components, in a move to cut costs and boost production efficiency. The new SL and GT will be built alongside each other at Mercedes’ plant in Sindelfingen, Germany.

Early plans to base a successor to the smaller SLC off the same underpinnings have been abandoned following a recent decision not to replace the junior Mercedes roadster due to dwindling sales.

Early prototypes of the new SL were spied testing on track with the new platform underneath a shortened S-Class Coupé body. The car is rumoured to run a transaxle arrangement with a dual-clutch automatic gearbox integrated within the rear axle assembly, like on the GT. However, the overall dimensions of the prototypes suggest the production version will be slightly larger than the existing SL, which is 4630mm long, 1870mm wide and 1310mm tall.

The adoption of the MSA platform is claimed to have had a positive effect on the styling of the new SL, whose proportions are said to be more in keeping with earlier incarnations of the classic roadster than the current model, which shares a platform with saloon models such as the C-Class, E-Class, CLS and S-Class.

A Mercedes source told Autocar: “The new platform has given us more freedom. There’s more distance between the front axle and the front firewall. This gives it more traditional proportions.”

The decision to replace the folding hard-top of today’s SL with a more compact fabric hood is also said to have provided greater scope in the styling of the rear of the new model. “It’s much more shapely, especially at the rear, because it is no longer dictated in height and width for the packaging of the hard-top roof,” the source added.

*SL to get hybrid line-up*

Mercedes plans to offer the SL with a limited range of hybridised in-line six-cylinder and V8 petrol engines in a line-up that’s likely to include both standard and AMG models.

The range is understood to start with an SL 450 EQ Boost model running a turbocharged 3.0-litre in-line six-cylinder developing around 365bhp, along with an added 22bhp in combination with an integrated starter motor.

Further up will be the SL 53, which will run a more powerful AMG-tuned version of the SL450 EQ Boost’s mild-hybrid drivetrain with around 430bhp and added 22bhp through electric assistance.

Among the V8-powered models will be the SL 500 EQ Boost. It is due to receive a turbocharged 4.0-litre V8 with a similar power output to the SL 53, but significantly more torque. Topping the range will be the SL 63. It is likely to be offered in two states of tune, with the most powerful model running a turbocharged 4.0-litre V8 capable of in excess of 600bhp and more than 30bhp of electric boost. It is unclear if Mercedes will continue with the V12-powered SL, although, given the potential output of the SL 63, it would seem unlikely.

All engines for the new SL will come as standard with Mercedes’ nine-speed automatic gearbox, with the AMG variants set to adopt the Speedshift electronics package for faster shift times. Suggestions are that Mercedes could offer 4Matic four-wheel drive alongside standard rear-wheel drive, although this has yet to be confirmed.

Despite the SL’s market repositioning, it won’t completely abandon the luxury focus, so expect the interior to be almost as opulent as Mercedes’ other high-end models. It will be more driver-focused than cars such as the S-Class Coupé, but there could still be plenty of the brand’s latest driver assist systems drafted in, including its semi-autonomous Drive Pilot function.

Additional reporting by Rachel Burgess

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