Aerodynamics and reducing lift on your saloon car
by Adian Yein Khalid

There was a discussion on the aerodynamic properties of our road cars the other day: What sort of body type is more aerodynamic? And do those GT rear wings really work?

Actually, liftback (aeroback) type body shells are generally more aerodynamic, but at a price: increased lift. Why is this?

Take a look at the basic shape, and you'll notice that it's a lot like an airplane's wing (aerofoil section). Recall that airplane wings are curved on the upper plane, and more or less flatter on the lower plane. This is to create a low pressure area by means of making the air that flows over the top of the wing to travel a further distance in the specific time that it takes the air to flow across the wing.

Remember science in Form 3? It's known as the Bernoulli Principle. Faster moving air has lower pressure than slower moving air. Therefore, an aerofoil section shape has a lower pressure section above the wing, which creates lift.

Apply this same principle to your saloon road cars. Don't compare a low-running DTM or Formula 1 car to your Wira Aeroback, as our road cars aren't low enough to make use of the ground-effect dynamics - more on this further on.

Simply, the air that flows over that long sculptured tailgate of Aerobacks creates a low pressure area that generates lift at high speed. How high a speed? Generally, aerodynamics come into play above 120kmh. No joke, when you take turn 12, 13 and 14 at the Sepang F1 Circuit, you will feel the difference between a Satria or Aeroback, and a Putra or a Wira sedan.

Next question I hear is: Why don't sedans have as much lift as Aerobacks?

Well, at the point where the roof ends and the rear window angles down steeply, separation of the airflow occurs, which means that the air is rather turbulent, negating any effects of lift. Unfortunately this also means that the total drag of the car is higher, therefore theoretically reducing topspeed, however this is countered as the airflow will reattached itself at the end of the boot section of the car.

And what of the assortment of rear/boot spoilers available on the market?

Lets start with the standard fitment bootlip that you'll find on some of the Wira sedans. The effect of this little item is again to reduce rear-end lift, but you won't experience any form of downforce. It forces the airflow to detach from the end of the bootlid, again creating increased turbulence to reduce rear-end lift. And you'll find that most of the Wira Aerobacks come with slightly raised spoilers. This again is able to reduce lift slightly and smoothen the airflow, but unfortunately it's realistically nothing more than cosmetic.

Mitsubishi EVO-style rear spoilers work apparently, but do not expect any great positive-downforce effects. If you're after realistic downforce figures, then get yourself one of those GT wings, BUT…