Do you remember when drag coefficient was something to shout about with cars? It was around the time when three-spoke aftermarket alloys were popular, if I recall correctly.

After the heady days of the Audi 100 (0.30 Cd) and the Vauxhall Calibra (0.26 Cd) aerodynamics seemed to go out of fashion, seemingly because people realised that if they cranked up the power they could overcome even the worst drag coefficient.

But because of a push towards eco-friendliness attention to slipperiness is now back in fashion, just look at BMW and Mercedes. One of the big selling points of the E-class coupe is that it is the world’s most aerodynamic car, which has a Cd figure of 0.24. There is even talk of a 0.20 Mercedes within the next five years.

2011 BMW M5 breaks cover

BMW estimates that a 10 per cent reduction in drag can reduce fuel consumption by 2.5 per cent and is concentrating on improving airflow underneath the car and around the wheel arches. Flaps and intakes in the bumpers and grille will help to direct air for best effect.

The bonus about all this is best illustrated by the new BMW M5. Along with controlled weight and smaller turbocharged engines improved aerodynamics mean we save fuel and reduce emissions in a car that is more powerful and faster.

With this in mind the days of etching a car’s Cd on to its windows may be back, but hopefully without the three-spoke alloys.

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