The first-generation Mercedes-Benz SLK was presented at the Turin Motor Show in April 1996 and was launched on the market in autumn of the same year. It added a new dimension to series of "SL" (sporty, lightweight) vehicles, the K in the name "SLK" standing for "kurz" or "short". The engineers were uncompromising when it came to safety, comfort, environmental compatibility and suitability for everyday use. They developed a vehicle that differed from other roadsters in its class in many respects, the most noticeable, perhaps, being the vario-roof – a steel roof which could be fully retracted into the boot.
A near-production study of a sleek but safe roadster with the now familiar name "SLK" had been exhibited at the Turin Motor Show two years earlier in 1994. Since then the SLK had caused a sensation wherever it appeared. At the Paris Motor Show in October of the same year a further study appeared, this time featuring one of the most spectacular details of the subsequent series-production vehicle: the vario-roof.
In Germany the SLK was available in two variants: the SLK 200, featuring a 2.0-litre four-cylinder engine with an output of 100 kW (136 hp), already familiar from the C‑Class and E‑Class, and the SLK 230 KOMPRESSOR, with a turbocharged 2.3‑litre four-cylinder engine that delivered an output of 142 kW (193 PS) and also featured in the C 230 KOMPRESSOR. A 2.0-litre variant of the supercharged engine was developed for Italy, Portugal and Greece. This had an output of 141 kW (191 hp) and, in addition to powering the SLK, was also fitted in an export version of the C-Class Saloon.
The supercharged engine not only delivered more output than a comparable naturally aspirated engine but beefier torque too. In the SLK 200 KOMPRESSOR the figure was 270 newton metres and in the SLK 230 KOMPRESSOR 280 newton metres. With both engines this was available from as low as 2500 rpm and remained constant up to 4800 rpm. Both engines achieved a top speed of 231 km/h, and acceleration from 0 to 100 km/h took 7.7 and 7.6 seconds. The SLK 200 did not lag far behind: it offered 190 newton metres between 3700 and 4500 rpm, took 9.7 seconds to accelerate from 0 to 100 km/h and had a top speed of 208 km/h.
The fully retractable, electrohydraulic vario-roof was made of steel and folded away into the boot at the touch of a button, turning a weatherproof coupé into a roadster in next to no time. The mechanism was sheer poetry. First the two-part roof pivoted upwards. At the same time the parcel shelf disappeared beneath the boot lid, which tipped backwards and upwards in order to make room in the boot for the roof. The roof folded and glided into place, the boot lid closed, and the parcel shelf returned to its original position. The whole process took just 25 seconds.
The two fixed roll-over bars, positioned behind the seats, were made from heavy-walled tubular steel (diameter 40 millimetres, wall thickness 2.5 millimetres) and tapered towards the top. Together with the particularly robust A-pillars, they ensured the exceptional standard of safety for which open-top Mercedes-Benz vehicles are known. The roll-over bars were bolted to a robust cross-member towards the top of the rear bulkhead. The A‑pillars concealed two tubes with diameters of 20 and 25 millimetres which were inserted into one another, shaped and welded to the outer shell of the A-pillars using special fittings. Each of the tubes had a specific task in the event of a roll-over: the upper one reached as far as the frame of the windscreen, improving its rigidity, while the lower tube reinforced the A-pillar at dashboard height. Other safety features included two airbags (driver, passenger), automatic seat belts, belt tensioners and belt force limiters. Sidebags, which unfolded between the occupant and the door, were available as an option.
The front-end structure of the SLK saw Mercedes-Benz's first use of a newly developed ellipsoid bulkhead. In the event of a frontal impact, the front-facing bulge of the bulkhead increased the front crumple zone, helping to preserve the footwell and reduce the risk of foot injuries. In a frontal collision its shape diverted the impact forces to optimum effect – its curved outer edges formed a direct connection between the front longitudinal members, the inner connecting members in the floor assembly and the outer longitudinal members in the door sills.
Despite the absence of a roof assembly, the vehicle body offered the impressive rigidity and strength of a saloon. This was the result of a large contact area between the longitudinal members and the floor assembly, numerous cross-members in the front and rear of the body and between the A-pillars and the use of a multi-part floor assembly with a central tunnel and side members in thick sheet steel.
Another new feature was electronic child seat recognition in the passenger seat. The system prevented activation of the passenger airbag if a special Mercedes child seat with transponder was fitted.
Behind the welded interior bulkhead, between the fuel tank and the load compartment, was another partition, made from diecast magnesium, a material which underlined another of the body engineers' key development goals – lightweight construction. The same material was used for the cover behind the roll-over bars. This was the first time that Mercedes‑Benz had used lightweight magnesium, a material that allowed a weight reduction of up to 50 percent compared with steel, in a series-produced vehicle. Magnesium was also used for the engines' cylinder head covers. These and other measures ensured a low overall weight of just 1270 kilograms for the base version.
The SLK's lightweight construction and its aerodynamic design – the SLK 200 had a Cd value of 0.33, making it one of the most aerodynamically efficient cars in its class – helped ensure that fuel consumption was low. The SLK 200 consumed 9.1 litres of premium unleaded petrol per 100 kilometres, the SLK 200 KOMPRESSOR 8.5 litres of Super Plus and the SLK 230 KOMPRESSOR 8.8 litres of premium unleaded (each of these figures representing NEDC combined consumption).
The SLK was the first Mercedes‑B enz passenger car model to be supplied without a conventional spare wheel. In Germany the car came as standard with TIREFIT tyre sealant which was designed to seal damaged tyres so that the vehicle could be driven to a workshop. In many other countries this was available as an option. The system included an electric air pump which was connected to the on-board power supply via the cigarette lighter. Omission of the spare wheel ensured a boot capacity of 348 litres (VDA measuring method) – an impressive figure for this vehicle class. And on top of this, the spare wheel recess was still available and could be used to house the collapsible spare tyre, available as an option in certain markets, and an electric pump, or a practical luggage recess. With the roof open, the boot capacity was 145 litres.
Standard equipment for the compact Mercedes roadster included power steering, light-alloy wheels, sports seats, power windows, a leather steering wheel, a drive authorisation system, a draught-stop and central locking. There was a choice of eight different paintwork colours and five interior colours. The SLK marked the first time that the designers had used a two-tone interior: while the upper part of the dashboard, the steering wheel rim and the sides of the seat cushions were in anthracite, the door panels, cockpit, glove compartment lid, centre console and shift gaiter were in the selected appointments colour, customers being able to choose here between red, blue, green, beige and anthracite. This two-tone colour scheme underlined the roadster's youthful look.
The same could be said of a series of other interior design features: for example the soft ruffled pockets in the doors, the stainless steel pedals and door sill panels with their distinctive rubber studs which were reminiscent of race cars from a bygone era. The nostalgic look continued with the ivory-coloured, chrome-ringed cockpit dials and the red needles of the speedometer, rev counter, fuel gauge and coolant temperature gauge. The carbon fibre design of the control panel in the centre console, the air vents and the door openers was in keeping with the roadster's distinctly sporty look.
For an even sportier exterior design, the SLK could be factory-fitted with the AMG body design package, consisting of a front apron with integral circular fog lamps, side skirts and a rear apron, all painted in vehicle colour. A modified rear silencer with chromed tailpipes blended harmoniously with the rear apron. AMG light-alloy wheels, size 7.5 J x 17 for the front axle and 8.5 J x 17 for the rear, were also available. On the SLK 230 KOMPRESSOR these could be combined with wide-base size 225/45 ZR 17 tyres at the front and 245/40 ZR 17 at the rear.
The standard draught-stop was the result of a project by the aerodynamics engineers focusing on thermal comfort. Their aim was to reduce draughts in the interior of the Mercedes roadster when the vario-roof was open, even at higher speeds, offering the SLK's occupants optimum ride comfort. With the aid of a special test dummy whose plastic skin was fitted with electrical temperature sensors, the airflow specialists investigated draughts in the interior and developed an effective remedy: the frameless, fine-mesh, fabric draught-stop, which could be fitted between the roll-over bars in a few simple steps and ensured an even air and temperature distribution in the interior of the roadster. When the draught-stop was not needed, it could be folded up and was simple to stow.
Like its bigger counterparts in the SL series, the SLK, known internally as model series 170, was built in Bremen. In fact, as a result of huge demand, an extra 600 jobs were created there. This expansion of the production capacity was designed to reduce the inevitable backlogs in deliveries – as had been experienced with model series 129 – one drawback of prodigious market success.