Spoilers make cars go faster: True/False?

Race cars have rear spoilers. Race cars go fast. So that shiny new car with a rear spoiler must go like the clappers, right? Not as fast as a race car — it has no racing stripes after all — but plenty fast all the same. Of course today’s urban sophisticates aren’t sucked in by such subliminal marketing. But today’s urban sophisticates are too clever by half, because a rear spoiler really does make a car go faster.

A lot of people have heard that spoilers improve handling, which they do. A car is actually shaped a lot like an aircraft wing, with a shorter surface on the bottom than on the top. This means that lift is generated when the car is moving at speed which makes it less stable and reduces contact with the road, both of which are clearly bad things. A rear spoiler partly disrupts — or spoils — the flow of air that generates lift, pressing the car harder to the road. This was the original motivation for spoilers in racing.

That’s not all that a spoiler does, though, it also reduces aerodynamic drag. There are lots of things that increase the drag on a car, and today’s cars are covered in refinements designed to keep drag as low as practically possible. One of these is the rear spoiler, which helps draw air over the car with as little wake turbulence as possible, sometimes cutting drag quite considerably. Reducing drag makes a car more efficient, so that for the same engine power it will go faster.

Just whacking a shapely hunk of plastic on the back without careful design and testing will probably do more harm than good. But a well-designed spoiler reduces both lift and drag.

So spoilers do make cars go faster. And they make them more stable. I’m afraid that if you’ve been spreading the word that spoilers have nothing to do with speed your evangelising days are over. Don’t take it personally: it’s not the first time that a good story was spoiled by the truth.

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