The Saab 9-3 Sport Sedan holds best coefficient of .28

Posted on 01. Apr, 2007 by in 2000-2009, 9-3 SS, Sweden, Trollhättan, Sweden

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Photo Credit: Saab Automobile

The Saab 9-3 Sport Sedan sets itself apart from all other Saab models by obtaining the best drag coefficient (Cd) value of .28 This feat was due in part to a lot of time in refining the aerodynamics of the new model.

Here are some highlights that describe the Aerodynamics, Shape & Wind Noise.

Source: Saab Automobile

Aerodynamics
The final shape of the 9-3 Sport Sedan was the product of a painstaking liaison between body stylists and aerodynamicists. Saab’s decision to move from a hatchback shape with a relatively narrow track to a wider sedan format posed a tough challenge to the ingenuity of Chief Aerodynamicist Håkan Danielson and his team. Their mission was to produce a shape that cleaves the air as efficiently as possible, giving good high speed stability, optimised fuel consumption and low wind noise inside the car. The result is an impressive drag coefficient of 0.28, equalling best in class performance.

“We have managed to reduce the Cd value by more than 10 per cent compared to the old model, even though the increased width of this car means we are punching a bigger hole in the air,” says Danielson.

Slippery shape
The team concentrated their efforts on achieving a smooth airflow over, around, through and under the car. They focused on points of flow separation at the rear in order to reduce turbulence and improve stability by reducing the size of the car’s wake. The shaping of the side sills and the radius and curvature of the rear corner of the C-pillar also helps reduce drag.

The rear edge of the hood lid ‘kicks up’ to smooth the passage of air on to and around the windscreen. Thee team also worked hard to reduce disturbance where the bottom of rear window joins the trunk deck, a particularly sensitive area in ‘notchback’ shapes. The subtle upturn of the rear edge of the trunk lid is, in effect, an integral ‘lip’ spoiler which helps reduce the size of the car’s wake, the area of turbulent air that trails behind the car at speed.

Good airflow management also contributes to keeping the windows of the car as free from grime as possible. For example, the door mirror casings have a small spoiler-like profile in the bottom surface to reduce contamination of the side windows.

In addition to its excellent low drag shape, the team have made major strides in improving stability. Compared to its predecessor, lift forces at the rear axle – an important determinant of high speed stability, especially under braking – are reduced by an impressive 30 per cent. A value of 0.11 Clr (coefficient of rear lift) is again on a par with best in class.

Low wind noise
Special attention has been given to reducing wind noise. The adoption of monoside body pressings, with inset doors and seals, makes a significant contribution. There has also been fine tuning of the A-pillars and door mirrors.

The traditionally deep curvature of the windscreen reduces the acceleration of the airflow as it approaches the A-pillars, which have a flattened radius where they connect to the windscreen to minimise airflow disturbance. The bottom edge of the door mirror casings is also extended rearwards by 5 mm to further reduce the likelihood of wind noise at speed.

Good airflow management even plays a safety role in the 9-3 Sport Sedan. The ‘wraparound’ rear light clusters have an optimized radius that gives a distinct separation for airflow along the side of the car. However, careful shaping of the angle actually helps the air ‘turn the corner’ first before it separates. The creation of a flow over part of the light clusters has the effect of helping to reduce the build up of road grime, which can impair the visibility of the lights.

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