We’ve all seen them: the enormous pieces of scaffolding bolted to the boot of a car. Sometimes they look sleek and stylish, often they look plain ridiculous. But do they actually work?

Well, that depends.

Aerodynamics is a complicated science, one far too technical for my simple brain. What I do know is that rear wings only work if they are designed and installed properly. That means, they must interact with the airflow over the car in a way that exerts downforce on the rear of the vehicle. The wrong spoiler on the wrong angle can create lift, which is exactly what you don’t want.

However, as a general rule of thumb, this act of downforce doesn’t usually begin to occur until the vehicle is travelling at speeds in excess of 100km/h, making spoilers essentially useless at road legal speeds.

So for street use, a spoiler is little more than a design feature on a car, an add-on designed to attract attention and tell the world your car is fast.

For cars used on tracks (or in illegal street races, if one was into such things) spoilers become essential.

The downforce created pushes the rear of the car down, making the rear tyres more effective in maintaining traction. Down fast straights and through high-speed cornering this keeps the car stable and allows the driver to control the vehicle at higher speeds.

Some modern, high-end rear wings can also flip their spoiler deck vertically under braking, creating an air brake to slow the car even faster. The Bugatti Veyron is one such car to feature this.

But for general, legal street driving spoilers are usually useless. Aerodynamically it is doing nothing as you pick your kids up from school and chug away at 40km/h. But hey, it looks cool and that’s important!

See the slideshow below for what happens when you type “stupid spoilers” into Google image search.