- Numerous innovations from the automatic roll-over bar to the integral seat
- Debut of the twelve-cylinder engine in the SL in the 129 series
- Official AMG versions available for the first time
At the 1989 Geneva Motor Show Mercedes-Benz presented an SL which was a new car in every respect. The first models were the 300 SL, 300 SL-24 and 500 SL. Internally the series was designated R 129. Unlike the predecessors, its production did not take place in Sindelfingen, but in Bremen, for capacity reasons. Straightaway the response was extremely positive, and shortly after the presentation it was foreseeable that the planned annual production capacity of 20,000 units would be stretched to the limit for years and delivery periods of several years would have to be accepted.
The SL face has captured a permanent slot in the Mercedes-Benz model hierarchy over the decades. The new SL re-interpreted the traditional basic shape of the grille: within the radiator grille, organically integrated into the bonnet, the Mercedes star was complemented by horizontal strips made of anodised aluminium. Chief designer Bruno Sacco had done an excellent job. The stylistically assured, no-frills lines of the slightly wedge-shaped body, the flared wheel arches for the wide-base tyres, the half-spoilers forward of the front wheels, a very slanted windscreen, the skilfully modelled rear end and the standard-fit light-alloy wheels produce an exceedingly harmonic overall effect.
The aerodynamic fine touches, including underbody and airflow through the engine compartment, added up to a fuel-saving, speed-increasing Cd of 0.32 with the hardtop mounted. A Cd figure of 0.40 was measured for the open-top car with closed side windows.
“Car Design Award”
Hardly a year after its launch the SL was decorated with the international Car Design Award. The SL was the top choice of an eleven-member jury of journalists from ten countries, assisted by a representative of the city of Turin and one from the Piedmont region. The jury stated as reason for the award: “In the Mercedes-Benz 300 – 500 SL the ensemble of safety innovations …, exemplary ergonomic solutions, and stringent adherence to the traditional design culture of the manufacturer’s brand is convincing. The new SL embodies the most valuable elements of up-to-date industrial design, without losing the flair that distinguishes every sports cabriolet.”
The prerequisite for the proper operation of the fully automatic folding soft top under all conditions is the torsional stiffness of the body, which leaves nothing to be desired in this respect. To reduce the vibration and torsion characteristics typical of open-top cars, additional diagonal struts are fitted in the particularly critical areas of the body. In the front end the front axle carrier is connected with the door sills by two specially shaped struts. In the rear end two tubular struts between the door sills and the spare wheel recess serve the same function. Owing to these measures the torsional stiffness versus the previous model could be improved by around 30 percent and a saloon-like overall stiffness achieved.
New standards were set by this car also in the area of safety. The results of Mercedes-Benz’s rigorous frontal and rear-impact crash tests for the open-top vehicle were sensational and a clear proof of the scrupulous precision with which the developers had worked. The resistance to side impact went far beyond what the law required and once again set trends for the sensible design of all details, for instance the overlapping of the doors with the sills, the cross-bracing beneath the seats, including the stiff sides of the transmission tunnel, or the high-strength steel tubes inside the A-pillars, which can withstand a roof impact. This two-shelled structure of the front roof frame in conjunction with the bonding of the windscreen to the body results in very great stability even if a one-sided load is applied to the roof frame.
An integral part of the safety concept is the automatic roll-over bar which was realised in the SL for the first time in an automobile and has the purpose of protecting the occupants’ survival space in the event the car overturns. So as not to impair open-top driving pleasure with a permanently installed, rigid rollbar, a flexible solution was realised which activates the roll-over protection only if needed.
When not in use the safety bar, consisting of a U-shaped high-strength steel tube foam-padded with polyurethane, is deposited in front of the soft-top compartment, closing off the rear compartment towards the back and forming a level surface with the top well lid. When a roll-over threatens, the sensor-controlled roll-over bar is electromagnetically triggered, raised into position by the force of pre-compressed springs within 0.3 seconds and secured by pawls. The high-strength centre pillars, connected over a large area with the rear longitudinal members, serve as basis for mounting and as support. In addition to automatic triggering in an emergency, by means of a switch the driver can choose to raise and lower the bar slowly, with a hydraulic element carrying out the action.
The most advanced feature of the interior design were the integral seats of the SL, which are a technical masterpiece in their design and an important part of the safety concept. The seat frame and backrest are made of various special magnesium alloys executed in thin-wall casting technique. They incorporate the three-point seat belt with belt tensioner, the belt height adjustment, coupled with the head restraint adjustment, and electric stepper motors for adjusting reach, height and tilt of the seat cushion and backrest. Another important feature is the automatic positive locking of the backrest. The resistance of the seat in a crash is many times higher than the possibly occurring forces.
Twenty patents for solutions to various details went into this seat; its creator received the Paul Pietsch Prize and high prize money in acknowledgement of his pioneering work in 1989.