Thu
Jul 02 2009

Why aerodynamics are no longer a drag

Ollie Stallwood
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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About Ollie Stallwood

Did a degree in art history before writing about cars, so has an appreciation for the old masters - such as the Mk1 Golf GTI and the E30 BMW M3.

Comments

theonlydt July 2, 2009 8:57 PM

I think the aerodynamic improvements continued - despite not being used as an advertising line. It's difficult to get hold of data, but any that you do shows a gradual improvement in almost all makes/models through the 80s, 90s and "00s" with the design of cars. I remember the mark.... II? III? Escort was applauded for 0.34 down from 0.43! That was a long time ago...

Citytiger July 2, 2009 9:07 PM

If you look at the latest trend of eco vehicles, most manufacturers are carrying out aero tweeks to existing models to achieve better (greener) figures, dropping the ride height, adding diffusers, skinnier wheels, spoilers etc.  

shiakas July 3, 2009 1:37 AM

The Tatra 77 had a drag coefficient of 0.212... in 1934! To even advertise figures that don't even match that 75 year old one is ridiculous.  

macaroni July 3, 2009 8:39 AM

Like all trends, it became a big selling point and then the hysteria died and it became commonplace. See also turbochargers, 16v, 4x4 and safety. Hopefully the same will happen to this eco nonsense very soon.

David Targett July 3, 2009 9:49 AM

The relevant figure is CdA - multiplying the coefficient of drag by the car's frontal area to get the actual drag created. A BMW X5 could have an incredible Cd, but it would still take a lot of shove to push it through the air at motorway speeds.

noluddite July 3, 2009 12:59 PM

As you know, drag increases with the square of speed. With our traffic choked roads, and official consumption figures based around tests at fairly low speeds, it therefore is no surprise that manufacturers are now placing less emphasis on drag, and more on the drivetrain.

BadgerRacing August 4, 2009 6:09 PM

A friend works as an aero designer for a F1 team, and he says one of the biggest issues is with wheels - they are moving through the air far faster than the car body  itself, hence the covers this year.

It could be a just matter of years before the artful multi-spoke alloy is consigned to the graveyard of automotive design, to be replaced with boring discs in the name of efficiency.

Ben

www.clear-offset.com

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