Michael Scarlett on the advantages of Audi's aluminium alloy models
FROM NEXT autumn, some British executives could be driving saloons made of aluminium
alloy instead of steel. That is when Audi's A8 arrives in right-hand-drive form, priced at about £34,000 for the 2.8-litre V6 front-drive version, and £46,000 for the 4.2-litre four-wheel-drive V8.
Why alloy? All cars, and those in the executive car sector in particular, have become increasingly heavy with greater refinement and more passive-safety features.
Attempts to control weight to curb heavier fuel consumption and maintain performance tend to be well-intentioned but piecemeal. Audi has grasped the nettle because aluminium weighs one third that of steel for the same volume. Audi's problem was finding the best way of making the body-chassis. Light alloys are not as stiff as steel, so to get the same stiffness in a stressed-skin structure such as a car body extra alloy must be used.
When Honda produced its aluminium-alloy NSX super-fast sports coupe in 1989, the stressed-skin shell was reinforced at points where stiffness was particularly important. Audi, and Alcoa, its American light -alloy-making partner, chose a halfway house in structural weight efficiency. The A8 has a skeleton frame of hollow extruded beams joined with high-quality castings, on which the skin is fixed.
With such a frame, at the price of some extra weight, it is much easier to make the areas where load is applied - suspension pivots, door, bumper and engine mountings - strong and stiff.As a result, the A8 body-cum-frame weighs only 550 lb, against 770 lb for a BMW 7-series, or 800 lb for a Mercedes-Benz S-class. Yet Audi claims it is stiffer than any rival and even more crash-worthy.As a user, you are hardly aware of what the A8 is made of; all the aluminium is painted to the usual high standards of a fine car. It drives superbly in all respects, and is in most ways very quiet.
The 140 mph 2.8-litre version is a very good example of a front-drive large saloon with less of the performance loss you might expect compared to the 155 mph 4.2. Both cars ride well, and are proving to be a competitor to BMW, Jaguar, Mercedes and Toyota's Lexus.
