What Drives Us episode

Be Aware of Your Car’s Aerodynamics

16 May , 2016  

-Tony Schaefer

Anyone who has watched Star Trek: The Next Generation understands the futility of the sleek design of the Enterprise when compared to a Borg ship. I call it futility because someone spent a lot of time designing a sleek and aerodynamic design for a ship that will only ever travel in a vacuum, devoid of air (except, of course, when it’s crash landing on Veridian III).

My point here is that when there is no air, the cube shape of the Borg ship is equally as aerodynamic as any Starfleet vessel. Unfortunately, we do not maneuver our vessels in a vacuum; we have to deal with wind resistance and the impact it has on our fuel consumption.

Willie Yee’s Zhang Heng is exactly as aerodynamic as the starship Enterprise. In a vacuum.

Willie Yee’s Zhang Heng is exactly as aerodynamic as the starship Enterprise. In a vacuum.

Because we have to deal with air resistance, we must pay special attention to the way air flows around our cars. One thing is for sure: when a manufacturer puts a car into a wind tunnel, they don’t strap a Thule cargo carrier on the roof and a couple bikes onto the back. In order to earn the lowest coefficient of drag possible, the manufacturer tried to make their car as streamlined and “slippery” as possible. The goal is to disturb the air as little possible. Anything attached to the car will create a lot of disturbance and defeat the intentions.

In this article, we’re going to explore aerodynamics and how keeping your car free from external add-ons will make your car more efficient, improve your mileage, and save you gas money.

Let’s Geek Out on Aerodynamics for a Minute

Before we can delve into how things impact aerodynamics, we should sidebar for a minute and discuss what aerodynamics actually is. The easiest and simplest definition is that Aerodynamics deals with the way air flows around objects. As it turns out, the invisible air we take for granted does some really cool and strange things when objects are pushed through it.

For example, we don’t even consider it but when a car is being pushed through the air, the car is an object that wasn’t in that particular spot just a few second ago. So what? Have you ever pounded a nail into a piece of wood? That nail represents your car and the wood represents the air. The wood was perfectly happy at a state of equilibrium until you came along with your “I have a hammer and therefore everything is a nail” mentality. The nail is literally ripping the wood apart in the same way the car has to separate the air in order to pass through it. Nails are pointed to make it easier; clip the point off the nail and try again. The added effort required represents the wood’s resistance to a having a blunt object pushed through it. That’s visually the same thing as driving a Corvette compared to driving a Hummer.

Aerodynamics_FrontalPressure

Cars and air are different because the car keeps moving, which forces the air to collapse behind it. Air is, for most sakes and purposes, a fluid. Fluids take time to flow from one location to another. Therefore, when the air is collapsing behind the car, there is not an immediate “everything’s back to normal.” In fact, because of the car there is literally a hole in the air. Since the air cannot fill the hole as quickly as the car is moving, there is less air in the space immediately following the car, causing a zone of pressure that is negative compared to the surrounding air. This negatively pressurized space literally pulls the car backwards as it collapses.  The engine is working to push the car forward, splitting the air and at the same time, fighting the pressure attempting to pull the car backwards.  The goal, therefore, is to make one or both of these aspects more efficient.

Aerodynamics_RearVacuum

All manufacturers have to deal with Aerodynamics. Some don’t care; like when manufacturing extra-large SUVs and trucks. Some spend weeks or months in a wind tunnel tweaking and tuning every last bend and curve to improve the frontal and rear aerodynamics. The goal is to split the air and return it to normal as efficiently as possible. To that end, some people are so obsessed that they render – and sometimes create – their own impressions of what a super efficient, super aerodynamic car would look like.

Super-Aero Prius

OK. That should be enough to get the point across. The smoother and slicker the car, the more efficiently it will travel, the higher the mileage, and the more money you’ll save on gasoline.

For a really good explanation and much more information, go to BuildYourOwnRacecar.com. This is where I got the two images from. http://www.buildyourownracecar.com/race-car-aerodynamics-basics-and-design/

Remove Things from the Roof of your Car

The roof is a great place to lug a cargo carrier, kayak, Grandma, or whatever might need to be moved from one place to another, out of sight, and without taking up interior cargo room. But when these things are no longer needed, do yourself a favor and remove them. Too many times, it’s just easier to leave the things on the roof. It makes sense because it was probably difficult to get it all strapped in to begin with and removing it will be a hassle considering you’re going to need it again at some point. But if that “at some point” is in two years when you take another family trip, remove it.

Remove Things from the Back of your Car

By now, this should be pretty obvious. Not only does the bike rack full of bikes represent turbulence, it disrupts the air’s ability to smoothly exit the back of the car. This turbulence creates eddies that increase drag. When you’re not taking your bikes to go riding, remove them from the back of your car.

Make sure your Next Car is Aerodynamic

Perhaps your current car isn’t the most aerodynamic. There’s not much you can do about that now. But you can think about the future. Whenever you’re in the market for a new car, try to make sure the new one is more aerodynamic than the one you are trading in. By doing this, you will continuously make strides towards better mileage.

Summary

The study of aerodynamics is actually really neat and if you have time, dig into it. You should try to purchase vehicles that are designed with a low coefficient of drag because they most efficiently move through the air. Mounting things to the roof and/or the back of the car interrupts the smooth movement of the air, creates eddies and turbulence, and should be removed when not in use.

Table of Contents

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