Improve Gas Mileage - reduce sail and drag

Your gas mileage can be greatly improved if you reduce the amount of sail you have out there catching wind, and reduce the surface area you're dragging through the air. Reductions in these areas means improvement in miles per gallon.

The relative difficulty or cost of this tip is rated 1 to 10. A rating of 10 suggests that this tip is the most difficult or most costly. Expected savings are also rated 1 to 10. A rating of 10 suggests that this tip will provide substantial savings in fuel, money or both.

Reduce Sail

Think of a sailboat on the water. It is driven by that large sail sticking up high in the air to catch wind. The moving air performs work by pushing the boat.

Air you are moving through does the same thing with your car, except it usually performs work by trying to make it harder for you to move your car efficiently through the air. This costs money in terms of poorer gas mileage.

Of course a car doesn’t have a sail, but a luggage rack (loaded or unloaded) or something else strapped to the roof of your car or sticking out of your pickup bed is a smaller version of the same thing. It catches wind and makes you burn more fuel to overcome the resistance.

That’s why you see some people take out the tailgate of their pickup truck and replace it with a net, or simply ride around with the tailgate down. The net or open tailgate is supposed to allow wind to pass easily and reduce friction that the truck would otherwise have while driving with the tailgate up.

The idea is that less friction from air resistance will equal better gas mileage.

My friend Sean notes however, that the tailgate of the pickup truck in the up/closed position is somewhat more fuel efficient than leaving it open. Albeit counter-intuitive, it appears that a high pressure "air bubble" is trapped between the cab and closed tailgate, and that is more conducive to wind passing over the cab than it would be with the tailgate down.

I drive with my tailgate up anyway since it keeps things inside the bed, and reduces the chance of someone running into it at a stoplight, or while strolling through a parking lot. You might try it both ways to see which results in better gas mileage.

Regardless, vehicle designs are extensively tested to make them conducive to slipping through the air with as little effort as possible. Don’t inhibit the intention of the design by unnecessarily putting stuff on the outside of your car. It adds drag that interferes with getting better fuel economy.

Ever noticed that the large trucks, vans and SUVs have the worst fuel economy? This is due in part to their large flat surfaces that face oncoming air. This is the sail that they have to push through the air. Their poor fuel economy is also attributable to their weight, but sail is very important since it is affected by wind as well as speed of the vehicle.

The faster you go, the more influence sail and drag has on fuel economy. At very slow speeds, sail has almost no influence, so if you are puttering around at 25 mph, don’t worry too much about the amount of sail you have sticking up to catch the wind. Anything 40 mph or over will have a considerable influence on your ability to get better gas mileage.

Reduce Drag

An example of drag is driving with the windows open to stay cool in the summer. The open windows cause turbulence and this creates drag that the car has to overcome by using more fuel.

Remember, that noise is energy and it has to come from somewhere. You are paying in gas mileage for that wind noise that comes from an open window, so get better gas mileage by keeping the windows closed at highway speeds and use the air conditioner sparingly.

At slower speeds, the drag from open windows is much like sail, not any concern until you start traveling faster, so enjoy the fresh air.

Cost or difficulty: 1
Savings: 3

Done with Gas Mileage, take me back to Save Gas

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