Open-top motoring should be nothing but sheer pleasure: smelling the forests and meadows, hearing the birds singing, savouring the sound of the sea, feeling the warmth of the sun. And in spite of this proximity to the natural world, the occupants in the new SL do not have to relinquish comfort. Even at higher speeds they are largely unaffected by any strong winds. In this respect, just like its predecessor, the new luxury roadster is unsurpassed by no other open-top two-seater.
First and foremost it is the rigid aluminium bodyshell and – one of the brand’s hallmarks – sophisticated aerodynamics which ensure excellent comfort during open-top motoring. The designers’ intelligent and highly efficient work has resulted in superb aerodynamic properties for the SL in several respects. This means that the roadster earns top marks in no less than four important disciplines within its segment:
Best cd figure
Wind noise on a par with a saloon
Open-top motoring in maximum comfort
Best anti-soiling measures
Top-class: cd figure
The new SL shines with a cd figure of 0.27 (in the SL 350). Never before has a vehicle in the roadster segment achieved such a low cd. At the same time, the cLR value (the coefficient of lift at the rear axle), which is decisive when it comes to braking stability, is reduced by 0.01. This ensures a lower lift at the rear axle than at the front axle – which is important for comfortable, safe handling at high speeds and/or when there is a crosswind.
The fact that not only could the cd figure be cut to a record low but that it was also possible to reduce the wind resistance as a whole is even more astounding when taking into account the fact that the new SL’s frontal area is around four percent larger than that of its predecessor – due in part to its wider track. The product of the frontal area and the cd figure is, however, smaller.
Alongside a great deal of precision work, some of the other factors which contribute towards the low cd figure are:
a complete engine compartment and underbody panelling concept,
a spoiler lip on the top face of the boot lid,
a specifically designed spoiler lip on the tail light,
wheel spoilers in front of the front and rear wheels, and
redesigned exterior mirrors positioned on the beltline and with a mirror base specially optimised for the new SL.
A newly developed aero wheel which is part of the standard specification for the SL 350 also significantly reduces the wind resistance. Its rim section is largely closed, which means that the air flowing through the wheel to the exterior disturbs the air flowing past at the outside of the wheel than is the case with a conventional wheel. Together with tyres which have been specially tuned to this end, the aero wheel cuts the frontal area – which is also a decisive factor in determining the wind resistance – by 0.01 square metres. This pays off in the form of a reduction in consumption, which results in one gram per kilometre fewer carbon dioxide emissions.
In order to minimise wind resistance even further, the six-cylinder version of the new SL also employs an adjustable radiator shutter. This consists of a large number of louvres and is positioned between the radiator and the radiator fan. An actuator fixed to the engine’s cooling module can be turned to close or open the flow path of the cooling air. In this way the flow of air through the radiator and through the engine compartment can be regulated as necessary. This means that if the engine has low-level cooling requirements, the wind resistance falls, as do the fuel consumption and emissions.
Top-class: wind noise on a par with that in a saloon
Where wind noise is concerned, the predecessor of the new SL was already the benchmark in its segment. But its successor surpasses this high level. It is even possible to hold a conversation, listen to the radio and make a telephone call at high speeds. This is thanks in part to the new stand for the exterior mirror. Its shape facilitates optimum flow; both when the inflow is straight and in the case of crosswinds it causes only low wind noise.
The windscreen fitted with multi-layer foil also contributes towards the exemplarily low interior noise, combining a low component weight with good acoustic properties. Low-frequency sounds which can arise through vibrations in the vehicle’s bodyshell can to a large extent be prevented by the new SL’s aluminium bodyshell, through design measures which were taken into account and tested at an early stage.
Top-class: maintaining a draught-free interior
Even at speeds of around 200 km/h the new SL offers extraordinarily high comfort during open-top motoring, setting new standards here. When the vario-roof is closed and the side windows are lowered, a welcome breeze can be felt during hot weather. Even putting the side windows up tangibly reduces it. The occupants in the new SL enjoy a comfortable and virtually draught-free ride as soon as they use a draught-stop. A conventional, manually operated folding-frame draught-stop comes as part of the standard specification. Covered with a finely meshed, synthetic textile fabric, this draught-stop is mounted behind the seats and folded up by hand. It covers the entire area behind the seat backrests as far as the upper edge of the head restraints. It can be taken off and stowed in the boot as necessary.
A highlight comes in the form of a new electrically operated draught-stop which is available as an optional extra. This new development can also be extended and retracted by the driver or passenger during the journey, via a switch in the centre console. If the switch is operated, a trapezoidal frame is unfolded electrically, and when it reaches its final position a finely meshed textile fabric covers it, thus keeping the area behind the occupants virtually free of draughts. Once it has been retracted, the frame disappears completely in the rear compartment trim cover.
The innovative neck-level heating system AIRSCARF is also available as an optional extra. It emits preheated air from an orifice in the head restraint, and this warm air then wraps itself around the neck area of the occupants like an invisible scarf, therefore even making it possible to have the roof open when the temperature is cool, without any serious inconvenience.
Top-class: anti-soiling measures
Clean exterior mirrors and side windows are important factors where safety is concerned, yet all too often drivers cannot take them for granted. In this respect, the new SL profits from the detailed work carried out by the aerodynamics engineers and can to a large extent ensure clear vision for drivers – even when it is raining. This is achieved mainly through a precisely tuned package of anti-soiling measures. The A-pillar trim with a new shape features an aerodynamically and aeroacoustically tuned front edge and a water guide channel on the top edge prevent water from flowing from the windscreen to the side windows. The new exterior mirror has also been optimised for journeys during rainy weather. Water guide runnels and additional drip edges have been integrated into its housing, and to a large extent they keep water away from the mirror glass, and shift the break-away point of the droplets to the outside. As a consequence of the aerodynamic measures the side windows soil only slightly.