Tag Archive | "aerodynamics"

What They Didn’t Tell Us About Automotive Aerodynamics


Once upon a time cars had all the aerodynamic properties of your average house brick. They cut through the air like a knife through concrete. Manufacturers considered this and realised that they could make their cars more attractive and more economic by looking at the design.

At first it was all about the dart shape; obvious but uninspiring. Now, of course, aerodynamics has come of age and most cars now have slippery, complex designs. What the car designers didn’t say though, in some cases at least, was how dirty the back of the car would get. This is especially true of hatchbacks.

air2 What They Didn’t Tell Us About Automotive AerodynamicsThe aero properties of the hatchback are different from a conventional saloon because the more abrupt cut-off at the rear-end causes the air passing over the car to swirl around at the back. This in turn creates a vortex which sucks airborne dirt and contaminants back towards to tailgate and rear window. The result is instant oily dirt.

Some hatchbacks are worse than others by dint of their shape. With saloon cars the air passing over the vehicle tends to flow away in a sort of teardrop pattern. This is why you rarely see a saloon with a rear window wiper and why the glass seems to remain clear even in heavy rain.

All hatchbacks have one of the aforementioned wipers and also the means to squirt some windscreen fluid onto the glass. This is fine as it goes but it doesn’t really shift the more oily contaminants and the as a consequence the glass smears. Meanwhile the rest of the back of the car gets filthy and invites the odd rascally finger to write disparaging remarks about automotive cleanliness. They don’t tell you this at the dealerships do they?

The answer of course – and it’s the only answer because designers are not going to change their mind – is to wash your car more often. The downside of this is that the rest of the car is unlikely to be as dirty as the back hatch. This means the unfortunate owner is doing more car cleaning than is strictly necessary and that’s a pain. The alternative therefore is to buy a saloon. You might be considered a square who is not prepared to keep up with the modern vibe but at least you won’t have to wash the car so often.

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