Why that spoiler can be a real drag on fuel economy

From the grille to the tailpipe, there are a number of cosmetic features on a typical car that put form before function. The spoiler is one of them.

By Wheels Wheels.ca

Feb 21, 2012 4 min. read

Article was updated 12 years ago

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Most cars on the road today are designed with aerodynamics in mind, allowing each to scythe through the air like a dart while creating as little turbulence as possible — to a point, anyway — while also boasting sleek profiles, nice lines and a visceral aura of “let’s roll.”

But put aerodynamics above all other design considerations and we’d all be driving giant, 4-wheeled saucers that wouldn’t be particularly functional for transporting people and cargo nor look the least bit pretty.

Still, from grille to tailpipe, there are a number of cosmetic features on your typical ride that put form before function; style and sex appeal before fuel economy.

More: Five tips to boost fuel economy in your everyday car

More: Here’s one way to save on gas — but is it safe?

From simple to garishly effective, here are three modifications you can make to maximize fuel efficiency.

1. Ditch the wing and spoiler: As often as not, a car with a rear wing is a pretender. In many cases, wings are dysfunctional automotive affectations that actually create drag. The proper application of a wing is to create down force at high speeds, which is why they’re correctly utilized on race cars, supercars and high-performance sports cars for the purpose of maintaining traction while doing at least 120 km/h on a race track or the Autobahn. Otherwise, they just look cool as they drag along and suck gas for naught.

Meanwhile, a “spoiler” on a car, often confused with a “wing” for its similar intent and placement on the rear end, is likewise superfluous on regular passenger cars, crossovers, SUVs and, chuckle, minivans. The actual function of a spoiler is to simply “spoil” airflow that is otherwise generating “lift” on any car that happens to be shaped from font to back like the wing of an airplane that wants to get airborne. Basically stated, a wing pushes the rear end down where it belongs, a spoiler stops the rear end from lifting up. Both create drag and neither serve a purpose beyond vanity on a regular urban ride.

Then again, a car with a rounded trunk will often have — or have added — an understated spoiler, rear fairings or “turbulators” that are both subtle and effective in diffusing the vortex of air that will build up behind a rounded rear end.

2. Pan or dam for flow: As smooth airflow over the top and around the sides of your car is obviously important, so too is the flow underneath, albeit less obviously. The space between the road and your typical vehicle’s underbelly reflects an obvious need for clearance to account for lumpy roads, speed bumps and such. To one degree or another, this ground clearance also allows air to “pile up” amongst the various compartments and components underneath (transmission, exhaust systems, etc.) creating aerodynamic deficiencies. Consider a “belly pan” that, like it sounds, will provide a smooth surface for air to pass under more-or-less unopposed (trapped engine heat will need to be dissipated). Newer cars sometimes come factory equipped with this aerodynamic nicety.

A cheaper, less radical and slightly less effective modification (if your ride doesn’t already have one) involves the use of an air dam or “diffuser” up front. These will direct airflow off to the sides of the car, though they have a tendency to scrape on steep driveways and speed bumps.

3. De-spoke the wheels: Wheels and the wells in which they reside need to be there, obviously, though they do tend to cause a lot of drag. You can reduce this greatly by losing the spoked wheels and all that “pimp” cachet and consider “racing disk” hub caps instead.

Distinguished by their utterly smooth, slightly convex shape and frequent appearance on “cars that go really fast,” these aerodynamic hub caps are becoming more and more popular on rides that just want better fuel economy at regular speeds, and where they’re also known as “moon disks.”

By a similar token, closing off the rear wheel wells might make your car look like something out of the ‘50, but it will effectively streamline your car as well. And, depending on where you do your aftermarket shopping, they can sometimes look pretty serious. Many concept cars in recent years are also hinting at a return to closed wheel wells not so much for fashion sense, but common sense.
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