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A/C or Drag?

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posted on Sep, 10 2005 @ 07:22 PM
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Say I'm going between 30 and 50 MPH during a trip. Is there any way to find out (besides going through a tank of gas) which would be more efficient- opening the front windows (with the drag) or turning on the air conditioning?

Instinct would say "A/C takes a whole lot of power!" but then again, opening the windows seems like making the car a parachute to me. The news was giving tips on how to save gas/ money, and they mentioned window drag, so I decided to finally ask here!




posted on Sep, 10 2005 @ 07:31 PM
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Good question. Don't know the answer.

I'm going with rolling the windows down in a car without A/C as the most energy efficient because having A/C installed means there are extra belts and pulleys so that just driving around (even without it on) uses extra gas.

I don't think the wind drag from open side windows is very big with the wind whipping around the car, but that's just a guess.
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posted on Sep, 10 2005 @ 07:40 PM
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Using a vehicle's air conditioner will decrease mileage by as much as 20 percent. If it's cool enough, use the flow-through ventilation on your car instead of the air conditioner. At low speeds, it's effective to open a window.

When driving on the freeway, keep your windows rolled up. Opening a window at high speeds wlll create wind drag and lower your mileage. Instead, use the car's flow-through ventilation.
hribar.com...

Windows down and the drag coefficient at 30-50mph would not effect fuel mileage as much as A/C on.. 65-70mph it might though.

Windows down lets bugs in though...got skeeter spray?



posted on Sep, 10 2005 @ 07:40 PM
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I have an F-250 Crew Cab Turbodiesel, and drive quite a bit (40-50,000 miles a year) and I get better fuel mileage (about 1.5 miles a gallon better)with the A/C on, whether the windows are up or down with the A/C off.

My only explanation is that in an electronically controlled engine, the fuel metering must be altered somewhat (it's a diesel, so timing doesn't become a factor). This over several years of use... I will actually turn on the A/C in the winter just to get the "love."



4X4 Monkeys, not just for terrorizing L.A. traffic anymore...



posted on Sep, 10 2005 @ 07:48 PM
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That does sound bizarre MM.

I have a Civic Coupe automatic (4 gears plus overdrive). I use overdrive on the highway but often only use 4th gear in the city.

Anybody know which is better mileage in the city? It revs higher on 4th than overdrive I think.
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posted on Sep, 10 2005 @ 11:29 PM
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I know it's not very scientific, but Mythbusters did this exact problem one time. They put two vans on a track at the same speed, one with a/c on, one with windows down. The one with windows down went something like 8 more laps around the track after the one with a/c on ran out of gas.

Overdrive in automatics is like 5th gear in manuals. It's less power, but more efficient. For long drives or high speed drives it gives you better gas mileage, because the gearing doesn't make the engine rev as high.



posted on Sep, 10 2005 @ 11:49 PM
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I drive a dodge 1500 sport edition and only get 350 kms a tank with windows up, down, a/c on or off, hard on the pedal or easy, when it comes to gas mileage, I have no idea what that is.



posted on Sep, 11 2005 @ 02:33 AM
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cant remember where i seen it, but above 80 kms an hour it is apparently better to have the air con on

as for the gears, you have to pick the correct gear for the speed.

if you are doing 30 in top, and put your foot down to accelerate, you will use more fuel than shifting though 2nd 3rd and then to 4th.

in a higher gear the revs will be lower, but to accelerate you have to put ya foot down more, opening up the throttle and allowing more fuel to get used



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