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Old 05-30-2007, 10:25 AM   #1
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moonroof aerodynamics question

What is going to create more drag on my civic hb, a window open or the moonroof open? The moon roof on my civic is the type that opens outward creating a hole with a big wing behind it. I travel btw 40-50 mph. For that matter, should I just use the AC? There are lots of short steep hills so I'm thinking the AC would be a no-no but that is why I ask. I live in NC and after next week or so, being in the car with no AC or open window is going to be suicide.
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Old 05-30-2007, 10:47 AM   #2
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Not sure, but with the windows open I get a lot more air in the cabin.

I have a feeling the moon roof is aerodynamically more efficient for that reason.

When it gets hot for me, i'll have both open, unless the sun shines in on me. If its still hot, too bad, A/C it is. Sometimes u have to spoil urself!

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What is going to create more drag on my civic hb, a window open or the moonroof open? The moon roof on my civic is the type that opens outward creating a hole with a big wing behind it. I travel btw 40-50 mph. For that matter, should I just use the AC? There are lots of short steep hills so I'm thinking the AC would be a no-no but that is why I ask. I live in NC and after next week or so, being in the car with no AC or open window is going to be suicide.
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Old 05-30-2007, 11:17 AM   #3
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i just crack a front window and a back window and thats workin fine so far
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Old 05-30-2007, 11:48 AM   #4
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i just crack a front window and a back window and thats workin fine so far

Getting air throught my back window would more of a shatter than a crack. Sorry, I couldn't stop myself.

I'll probably be turning on the AC soon anyway but I'll try to sweat it out as long as I can. By the middle of June I'll be waking to 75F with 80%+ humidity and a 20F rise through the day, I'm just delaying the inevitable.
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Old 05-30-2007, 01:27 PM   #5
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I live in NC too! It's absolutely unbearable to go without AC or fully open windows during the humid summer months. I'm a heat sensitive person anyhow, so driving with nothing on simply doesn't cut it. I believe the general rule of thumb is if you're going at city speeds, keep your windows down. It won't create enough drag to be a significant hindrance. If you're driving at highways speeds (I'd say 45 or over), you're better off to roll up your windows and turn on the AC. The Moonroof would be more aerodynamic I would assume, but for me it doesn't cut it. There isn't nearly enough air into the car by opening the moonroof for me.
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Old 05-30-2007, 01:36 PM   #6
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lol i live in IL and it gets friggin humid (liek today) and neither of my rides has AC and we see temps well above 85 (usually low 90's ) in the summer. its windows down all the time when it gets that hot. vent only makes it hotter...
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Old 05-30-2007, 02:04 PM   #7
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Time to be pragmatic... this is just a hobby for some of us. In my case, sweating before hitting the work parking lot doesn't make a lot of sense... don't get me wrong, I do run somewhat uncomfortablely hot in the cab a lot.... but only because this MPG thing is fun.... ie it is a hobby. But in the end, the dollar amount I would save by sweating instead of using A/C wouldn't even be noise in my $$ budget.... hell, my house pmt is $4K a month... I could drive a Hummer and not notice.... actually, I think some of the other members could also drive a Hummer and not notice, based on the amount of gas they expend running "experiments".... but this is a hobby, like I said :-)
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Old 05-30-2007, 03:22 PM   #8
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If the choice is an outward-opening roof or an open side window, I'd pick the window. Both will increase Cd, but the open roof also increases A and will set up some pretty strong vortices from its trailing corners at speed.
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Old 05-30-2007, 08:33 PM   #9
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Your car's roof slides open externally?
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Old 05-30-2007, 09:20 PM   #10
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lol i doubt that will cause any significant air drag...most of the air is getting hit on the huge winshield not a cateteria tray sized piece of glass barely opened.
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