Modern, elegant, dynamic and yet clearly part of a great tradition: the SL Roadster from Mercedes-Benz was one of the biggest sensations at the Geneva Motor Show in March 1989. This sports car (model series R 129) first appeared in the 300 SL, 300 SL-24 and 500 SL variants, with several models being added in subsequent years through to the SL 73 AMG in 1999. The R 129 was the fourth generation of the SL-Class since the legendary gull-wing Mercedes-Benz 300 SL of the 1950s. In 2001, the 129 model series was replaced by the 230 series.
The SL models in the 129 series featured compelling technical innovations and a good balance between classic elements and new design. However, this generation of sports car also involved two changes to the SL tradition: firstly, the SL was built in Bremen rather than Sindelfingen and secondly, the Mercedes-Benz nomenclature was revised while the R 129 was being produced. In the summer of 1993, the Stuttgart-based brand adapted the model designations for its open-top sports cars to the nomenclature initially introduced for the C-Class and used up to the present day. From then on, the legendary abbreviation “SL” would appear in front of the three-digit number that indicates engine displacement. The 300 SL thus became the SL 300, making the300 SL from the 129 model series the last Mercedes-Benz sports car for the time being to bear this legendary model designation.
The automatic roll-over bar is debuted
Harmony was the hallmark of the modern new design elements that were introduced. Although dispensing with the traditional chrome surround around the SL radiator grille, with its fluid wedge shape the R 129 clearly followed in the tradition of its predecessors. Elegant design was backed by the concept of an automatic roll-over bar which only deploys in an emergency. Normally, it was not possible to see the protective structure when the car was being driven with the top down. If there was a danger of overturning, however, a sensor released the locking mechanism on the bar by electromagnetic means and the integral support rose in just 0.3 seconds. The driver could also deploy the bar hydraulically as required. The automatic roll-over bar in this form on the R 129 was an international first in automotive engineering.
In addition to the roll-over bar, the windscreen A-pillars made of high-strength steel, the twin-shell front roof frame and bonding the windscreen to the vehicle body contributed to a very high standard of safety on a par with that of the Mercedes-Benz saloons and coupés. The engineers achieved a high level of stability in the open-top sports car’s passenger compartment by making the floor assembly particularly rigid using high-strength sheets and large cross-members, as well as creating transitions that were resistant to bending from the A-pillars and rear side elements to the side longitudinal members. Thanks to the special design of the beading on the inside, the doors also acted as an impact-resistant connection between the front wall and centre pillars. The engineers developed the front-end concept on saloons further for the SL vehicle body in order to ensure maximum safety in the event of an offset frontal impact.
High standards of safety and comfort
The developers placed just as much emphasis on passenger comfort as on safety. One aspect encompassing both these areas was the new integral seats featuring excellent ergonomics for relaxed travel on long journeys. Due to their load-bearing structure and high transverse rigidity, they also offered enhanced protection in the event of a side impact. The load-bearing seat frame consisted of five die-cast magnesium parts and included the seat belt system with belt tensioner, seat belt height adjustment coupled to headrest adjustment, plus fully electric adjustment.
The new electrohydraulic soft top offered great convenience: it opened or closed within 30 seconds at the touch of a switch. When the top was down, another innovation came into play: the draught-stop, a screen which lets air through and can be attached to the roll-over bar in a flash, thereby minimising wind noise and draughts. As standard, the new SL models had electric windows and electropneumatic central locking. Electric steering column adjustment was initially restricted to the 500 SL.
A roadster featuring the torsional strength of a saloon
The roadster’s ride comfort was improved by installing additional diagonal struts and other reinforcements which optimised the vibration and torsional characteristics typical of open-top vehicles. The engineers’ expertise paid off and the torsional strength of the new roadster was 30 percent more than that of the preceding model and now equivalent to that of a saloon.
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