I n the wind tunnel studies carried out by Ricardo AS&A
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drawbars were shown to have better potential for aerodynamic savings than either rigids or articulated vehicles.
Expressed in terms of the drag factor (Cd), which is a measure of the ease with which a vehicle moves through the air, an artic achieved around 0.4, a rigid 0.33, and a drawbar 0.31; the lower the figure, the less drag there is holding the vehicle back.
Design consultant Vol Dare-Bryan says The Body Shop drawbar falls short of this ideal figure: "We knew that this was the worst example of a drawbar — one it's a demount, and two it uses a turntable trailer. Another difficulty was that both truck and trailer have a tail-lift." He estimates the actual Cd to be between 0.4 and 0.45.
The main principle behind the modifications is to keep the air flowing smoothly, and close to the contours of the body: "Good
• 'attachment to the box is vital for low drag," says Dare-Bryan. For this reason the design uses the gap between truck and trailer to keep the air close to the trailer body; on an artic the air tends to detach itself towards the rear of the trailer. This is done using a roof slope in