Mercedes-Benz will adopt aluminium body technology for its next-generation SL sports car, joining Aston Martin, Audi, Jaguar and Rolls-Royce as the fifth premium car maker using the weight saving material.

Mercedes has chosen a spaceframe based alloy construction, according to well placed sources, that makes it closer to Audi and BMW's technology, rather than the bonded and riveted structure used by Aston Martin and Jaguar.

To reduce the risk of production delays while the new technology is ramped up, a problem that hit both Audi and Jaguar when they first introduced alloy bodies, Mercedes will prove the new body construction on a limited edition luxury sports car, named SLC and code named R197.

The SLC borrows the basic technology of the SL but will have a completely different body and is due for launch in 2010, two years ahead of the SL, project R231.

In this sense, Mercedes is following a similar industrial strategy to BMW, which proved its alloy spaceframe on the low production Z8 before transferring the technology to Rolls-Royce.

Mercedes' iconic luxury sportscar should benefit in several ways from the lighter body — more agility, better performance and improved fuel economy.

A switch to alloy for the Merc SL's body structure should make substantial savings in the current car's kerb weight, which ranges from 1,750kg to 2,045kg depending on engine and trim.

Typically an alloy body in white is 40% lighter than an equivalent design in steel, a reduction that translates into a kerb weight saving of around 10 to 15%.

When Jaguar launched the alloy XK in 2005, it benchmarked the new 'complete body' weight of the convertible at 345kg, against 425kg for the Merc SL and 420kg for the BMW 6-Series.

Weight savings might be a little harder for Mercedes to achieve because today's SL already uses alloy front wings (fenders), bonnet (hood), doors and roof.

Both the Mercedes sports cars will be based around the same basic component set of powertrains, axles and sub-systems.

But each will have its own unique body structure and styling. The SLC, for example, has two potential design directions - a 'retro look' like the iconic 1950's 'gullwing' SL or an up-to-date avant-garde look.

As a result the SLC will be front engine and rear drive, rather than the mid engine layout reported by the specialist motoring press. It also means that the SLC will not be a variant of the forthcoming McLaren family of mid engine sports cars planned to follow up the SLR super car.

The SLC project is also being handed over to HWA, a new company set-up near Stuttgart by Hans-Werner Aufrecht, one of the co-owners of AMG. AMG is now wholly owned by Mercedes. HWA is building a brand new factory in Affalterbach to build the SLC.

Although HWA is also making key daily engineering decisions, the project is firmly under the control of Mercedes.

According to sources familiar with Mercedes' plans, annual production of the SLC is planned at between 3,000 and 4,000, a fraction of the SL's 50,000 to 60,000 a year figure.

As a result it will have a more exclusive market positioning, and will use higher output versions of the extensive engine range planned for the SL.

These are likely to be AMG-sourced V8 and V12 engines. A new six litre V8, the M157 series, is under development and a twin turbo version is in development with 600bhp.

Julian Rendell

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