Audi has developed a version of the A6 Avant designed to be usable as a high-performance estate car and an off-roader, by adding an electronically controlled air suspension system allowing different ride heights.
The company has produced four-wheel drive cars since it launched the quattro for world rallying 20 years ago. Until now, it has used the quattro system to enhance performance and stability rather than for off-road use.
To work as both, the Allroad quattro had to overcome the conflict between high-speed stability and rough-surface clearance and traction. The four-position, height adjustable suspension system is the key to this.
The suspension layout is similar to that of the normal A6, but the Allroad uses air struts as the springing and height adjustment medium. The system consists of the struts, plus an air supply unit and electronic control unit.
Four ride heights can be selected, manually by dashboard buttons within certain limits, or automatically depending on speed by the electronic control.
The low level position, with 142mm clearance, is for maximum high-speed stability (especially cornering stability) with minimum drag, and is intended for speeds over 75mph. Two second position, which is, 25mm higher, is for normal road driving at less than 75mph. Level three, a further 25mm higher, is for mild off-road terrain at speeds of up to 50mph, while the highest level, with 208mm clearance (almost as much as a Range Rover or Discovery), is for the roughest going.
The highest two settings are selected manually. The height controls are fail-safe and are overriden by the control unit depending on speed. The Allroad adopts its lowest level automatically above 75mph and prevents the two highest settings being selected above 50mph.
`Allroad’ tyres combine the durability and traction to cope with rough and soft terrain and are rated for on road speeds of up to 155mph. Traction is enhanced by the EDL electronic diff lock, which uses selective wheel braking to find traction.
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