Mercedes-Benz SLR McLaren Roadster In Detail

Press Release

High-tech materials for excellent torsional stiffness and exemplary occupant protection

• Carbon-fibre-reinforced body, ceramic brake discs
• Rigidity and crash safety of the highest order
• Comprehensive safety system with adaptive front airbags

Many things seem impossible - until someone proves otherwise. The new Mercedes-Benz SLR McLaren Roadster rebuts a long-standing prejudice, by demonstrating that an open-top high-performance sports car can be every bit as torsionally stiff as a closed coupé. The proof of this is outstanding handling characteristics and undiluted open-air driving pleasure to way beyond the 300 km/h mark, paired with excellent comfort on long journeys and unrestricted practicality for day-to-day driving, which together makes the new Roadster an open-top super sports car with a difference.

Underpinning all of this is the systematic and intelligent use of high-tech materials for the body and safety technology. As in the Coupé, the bodyshell of the high-performance Roadster, including the front-end and rear-end structure, the passenger cell, the swing-wing doors and the bonnet, is made entirely from carbon-fibre-reinforced plastic. This lightweight yet extremely rigid material originated in the aviation and space industries and has also proven its benefits in today's Formula 1 racing cars. Compared to steel, the high-tech material represents a weight saving of around 50 per cent.

Scientists at DaimlerChrysler Research played an instrumental role in the development and transfer to series production of carbon-fibre materials in the aviation industry, where they are used predominantly for fins, rudders and landing flaps. Quite apart from this, the experts at Mercedes-Benz and McLaren have gained extensive experience with this exotic material, as well as acquiring tremendous expertise in its processing, from their work on racing cars. This invaluable know-how has also been put to good use in the new Mercedes-Benz SLR McLaren Roadster, whose entire body harnesses the benefits of carbon-fibre-reinforced plastics (technical abbreviation: CFRP). Only the two engine mounts are made from aluminium. Even in super sports car circles, such extensive use of this expensive, high-tech material is still somewhat of an exception.

Carbon-fibre materials for low weight and high torsional stiffness

Mercedes-Benz and McLaren opted for widespread use of CFRP because of the evident beneficial effects carbon fibres have on rigidity and energy absorption. What's more, components made from this material weigh up to 50 per cent less than comparable steel components offering the same strength and as much as 30 per cent less than aluminium components. This makes CFRP the material of choice for manufacturing high-performance cars, because lower weight not only means lower fuel consumption but also outstanding transfer of power to the road. The lower the mass that has to be accelerated and braked, the better the agility. Owing to the consistent use of carbon-fibre-reinforced plastics, the primary structure of the Mercedes-Benz SLR McLaren Roadster is indeed considerably lighter than the conventional steel construction of a comparable front-mid-engined vehicle.

Intelligent advance in carbon technology

Compared to the Mercedes-Benz SLR McLaren, which marked the first ever use of carbon-fibre technology to such a large extent in series car production, the way in which the material is applied has undergone further advancement for the Roadster. By optimising the arrangement of the different layers of carbon-fibre matting, the engineers were able to minimise the unavoidable weight increase produced by the Roadster's roof without any loss of strength. This allowed the high-performance Roadster to retain an exceptionally high, coupé-like level of torsional stiffness that is unprecedented for a cabriolet but without any significant increase in weight, despite the mechanism for the soft top.

The roof's design meant there were other components in the Coupé that the design engineers were unable to transfer directly either: the A-pillars with their integral steel reinforcements, as well as the windscreen frame, the rear wings, the boot lid and the swing-wing doors have all been redesigned, although they continue to be made from carbon-fibre-reinforced material of course. In contrast to the Coupé, the unmistakable swing-wing doors inspired by the legendary SLR racing car from 1955 - or the Uhlenhaut Coupé as it is affectionately known - have a frameless design on the new Roadster so as not to lose any of that open-air driving sensation. As on the Coupé, the doors are attached to the front roof pillars and swing forwards and upwards through an angle of 107 degrees when they open. This door concept makes for a sensational appearance.

CFRP achieves high energy absorption capacity

Apart from their extreme stiffness, the state-of-the-art carbon-fibre-reinforced materials are also renowned for their excellent energy absorption. The absorption capacity is around four to five times higher than that of metallic materials. Formula 1 constructors have been exploiting this quality for several years, manufacturing the crash structure of their racing cars from CFRP. It is primarily as a result of this that the risk of injury in high-speed accidents in this Blue Riband motorsport event has dropped significantly.

The monocoque - or, to put it another way, the passenger cell - of the new Mercedes-Benz SLR McLaren Roadster is also made entirely from this high-tech material. In the event of a head-on, side-on or rear-end collision, it offers the passengers a highly rigid and hence secure survival space.

The new A-pillar, with its additional internal reinforcement in the form of a high-strength steel tube, also has a role to play here. The arrival of the Mercedes-Benz SLR McLaren Roadster thereby marks the series-production debut of a highly complex steel/carbon-fibre compound that combines high strength with the elasticity required for safety reasons. Fixed rollover bars behind the seats complement the safety concept. They ensure the passengers are afforded an outstanding level of protection even if the vehicle should turn over.

Carbon-fibre crash elements in the front structure

At the rear, two internal side members made from laminated carbon fibre and a robust cross member assume the task of energy absorption in the event of a crash. In an impact from the side, the occupants are protected by the broad, low-set sills containing multi-shell deformable elements made from specially reinforced carbon-fibre materials as well as two aluminium sections incorporated into each door. The sturdy shell of the SLR seats also has a protective function in a rear-end or side-on collision and is likewise built from highly resilient carbon-fibre material.

It is in the front structure of the SLR bodyshell that the impressive safety properties of the innovative fibre composite are particularly evident. Here, two conical carbon-fibre-reinforced plastic elements - each approximately 620 millimetres in length, weighing just 3.4 kilograms and consisting of an encased inner web - are enough to absorb the full impact energy in a defined frontal collision without exceeding the tolerable deceleration threshold for the passengers. The carbon-fibre composite members are bolted onto the aluminium structure of the engine mounts behind them. This means that the Roadster, just like the Coupé, has a front crash structure manufactured entirely from carbon fibre.

In a collision, the fibres of the CFRP elements shred from front to rear, absorbing the energy of the impact with a constant rate of deceleration. Thanks to this steady deformation behaviour and the high-strength monocoque, the energy absorption of the CFRP side members can be precisely calibrated. The engineers achieve this, for example, by creating a constantly changing cross-sectional area for the components. This fine tuning means that the deceleration values result not only in predictable energy absorption behaviour but also in a weight advantage, because this design uses only as much material as is actually needed.

CFRP components in automated series production

Carbon-fibre composite components for racing cars and for the aviation and space industries are generally manufactured by hand - a time-consuming process. By contrast, many of the carbon-fibre components for the SLR Roadster are manufactured in an automated series-production process. To do this, the Mercedes engineers divided the manufacturing process into separate stages, with manufacture of the preform being followed by impregnation with resin and hardening.

In order to allow extensive automation of the manufacturing process for the carbon-fibre preform, the materials experts at Mercedes-Benz studied the work of their colleagues in the textile industry and adapted the highly automated manufacturing methods used in this sector, such as sewing, knitting, weaving and braiding, for the processing of high-performance CFRP fibres.

To take an example, the web in the middle of the SLR's side members is formed from several layers of carbon fibre placed on top of one another and sewed together by machine. Once the piece has been cut to shape and the ends folded up to form a double-T section, the web blank is inserted into a polystyrene braiding core. Next, a specially developed braiding machine forms the braided side member casing around this core using 25,000 extremely fine, individual carbon filaments which unwind simultaneously from 48 reels. This technology allows the fibre material to be braided around the core at a precisely calculated angle to create the required contour. Several layers are even laid on top of one another in certain areas, depending on the required thickness.

In a further manufacturing process, a computer-controlled tufting machine joins the inner web to the braid of the side member. The braiding core is then removed and the preform for the side member cut to the correct size. Finally, the preform is injected with resin.

Several patented solutions had to be developed and tested in order to ensure short cycle times and high repeat precision for this manufacturing process – both of which are crucial for series production. The manufacture of the complex fibre structure of the side members using a braiding machine requires a cycle time of just twelve minutes, which illustrates the potential output that this innovative manufacturing technology offers.

The British company McLaren Composites also manufactures over 50 components made from carbon-fibre and glass-fibre-reinforced plastics for the high-performance Roadster. Here too, familiar processes from the aviation industry were adapted and redeveloped. The degree of integration achieved in the manufacture of the bodyshell is particularly remarkable. The entire floor assembly, for example, including all support members and securing elements, is made in a single piece. High-strength bonding and riveting techniques ensure a lasting connection between the individual carbon-fibre components of the chassis and the body. The aluminium engine mounts are not only bolted to the carbon-fibre composite firewall, they are bonded into place too. The carbon-fibre structure includes integral metal link points for the aluminium and steel rear axle.