Maximum fuel efficiency: superlative aerodynamics minimise diesel consumption

• Good aerodynamics pay off every mile of the way
• Windscreens with pronounced curvature and large edge radii
• New aero windscreen wiper system with features adopted from motorsport
• Aerodynamically efficient rear end with recesses and airflow break-away edges
• Aerodynamic benefit: the Setra can save around 3000 litres of diesel

The new double-decker bus from Setra is a prime example of superlative aerodynamics. With a drag coefficient figure of C_d = 0.35 it sets a new benchmark in its segment. The exceptionally low wind resistance provides the basis for exceptional fuel efficiency: depending on its form of use, the Setra S 531 DT is up to ten percent more fuel-efficient than its already economical predecessor. This means that the new double-decker saves fuel and money on every mile of motorway driving, minimising emissions and saving resources in the process.

Good aerodynamics pay off every mile of the way

Images from the airflow simulation process demonstrate the new Setra's aerodynamic merits: at the front the airflow hugs the body, while at the rear the hefty touring coach does not leave any tell-tale wake behind it. Aerodynamics play a particularly important role for a heavyweight double-decker bus measuring over four metres in height, making the crucial difference in the face of the given cross-sectional area of the largest touring coaches. The difference that efficient aerodynamics make pays off for bus and coach operators every mile of the way.

The double-decker's development engineers were able to draw on the extensive wind tunnel findings acquired with the Setra ComfortClass 500 and the TopClass 500. These high- and super-high-deckers boast exemplary aerodynamics and lead the touring coach field with a drag coefficient of C_d = 0.33. 

Windscreens with pronounced curvature and large edge radii

The developers have pulled out all the stops for the new double-decker bus, too. The two windscreens are seamlessly joined and feature a more prominent curve. The front end of the bus has been extended by 85 mm for this purpose. The air is better able to flow around large edge radii.

Where necessary, for example on long-distance regular-service buses or inter-city buses, a destination indicator is installed behind the lower windscreen on board the new double-decker bus. Virtually no gaps remain between the body and the flush-closing doors and the driver's window. The leaf-shaped arms of the outside mirrors have also been aerodynamically optimised.

New aero windscreen wiper system with features adopted from motorsport

The aero windscreen wiper system on the double-decker bus plays a major role in reducing the vehicle's wind resistance. On the lower deck Setra employs the proven Aquablade windscreen wipers from the 500 model series. These are flat-blade wipers with integrated water guide and without disturbing stems.

The wiper for the upper windscreen came in for particular attention in designing the double-decker bus. The two-arm wiper system has been replaced by a centrally positioned one-arm wiper with flat-bar wiper blade. The vertical, aerodynamically optimised standby position for the windscreen wiper has been adopted from the field of motorsport. The wiped area corresponds to that of the previous system - whereby passengers from the second row on benefit in particular from the clear view which is now available through the middle of the windscreen.

The vehicle's aerodynamics are also optimised by features which are not immediately apparent. The rain troughs over the doors are only unfolded when the doors are opened, for example. This means that the vehicle's outer skin is smooth when the doors are closed, thus offering no wind resistance. Another feature which is invisible on the road but nevertheless effective is the underbody cover for the front-end assembly, which prevents turbulence.

In addition to reducing wind resistance and thus fuel consumption and emissions, the extensive aerodynamic fine tuning around the Setra's front end also minimises wind noise, thereby tangibly enhancing comfort for passengers and drivers.

Aerodynamically efficient rear end with recesses and airflow break-away edges

The Setra's newly designed rear end has also been developed with due regard to aerodynamic aspects. The roof has been provided with an airflow-optimised flue. The new corner pillars in the form of fins are recessed at the sides and feature sharp airflow break-away edges. These two measures serve to guide the airflow in a defined manner, thereby reducing turbulence as well as soiling. The measures increase the length of the rear overhang only negligibly, by 25 mm.

The double-decker bus is furthermore lowered imperceptibly by 20 mm from a speed of 95 km/h. In addition to the comprehensive fine-tuning work on the body, in this way the developers reduce the cross-section and thus the wind resistance.

Aerodynamic benefit: the Setra can save around 3000 litres of diesel

The comprehensive aerodynamic measures from the front to the rear reduce wind resistance substantially. The new double-decker's C_d figure stands at 0.35, setting the benchmark in this vehicle segment. And the Cd rating is far more than just a token value: according to Setra's experts, the reduction in wind resistance is accompanied by a drop in fuel consumption of around seven to eight percent in mixed touring use. On long-distance trips or in long-distance regular-service use, the savings are even in the two-figure percentage range.

At an annual mileage of 100 000 km, the new double-decker bus thus saves around 3000 litres more fuel than its predecessor. Savings are correspondingly higher when very high mileages apply in long-distance regular-service use. This cuts costs very noticeably, reduces emissions and saves resources.