So here's a good but dry video which shows in what way aerodynamis is impacted by driving with your windows down. The videos uses computer modeling. The channel overall is interesting
Driving with windows down and fuel efficiency
- Thread starter BMWTurboDzl
- Start date
Nick1994
$100 site donor 2024
I roll my windows down for 15-20 seconds after parking in the heat to let it out but I never drive with the windows down, it’s incredibly annoying. I’ve also had 5 cars with sunroofs and never opened them either.
edyvw
$50 site donor 2026
Always windows down, all four of them. Of course, if it is not too cold.
Mythbusters did this many years ago in testing. It's worth a watch
Patman
Staff member
I definitely get better gas mileage in my Civic with the windows down and AC off, compared to windows up and AC on. It’s about a 2-3 MPG difference at least.
Windows? What the hell are windows? I dont even have a roof over my head 98% of the time I'm driving. My friend will have all windows up and the A/C on when its sunny and 77F. I absolutely loathe driving with him.
But at what speed? At city speeds I can see a difference, but at highway speeds, not so much. )
Obviously windows down will have some impact on MPG but it's a surprisingly small effect. Auto Express magazine did a controlled test and this is what they found:
On the first run we had the front two windows open a third, and fuel economy was only 0.1 MPG off the baseline measurement. Going out again, with the two front windows fully open, it knocked the figure down by a further two-tenths so 0.3 mpg in total.
On the first run we had the front two windows open a third, and fuel economy was only 0.1 MPG off the baseline measurement. Going out again, with the two front windows fully open, it knocked the figure down by a further two-tenths so 0.3 mpg in total.
Well... I roll down windows only if I am going through a drive through and need to be handed something otherwise rarely if the interior is super hot, I roll down the windows long enough to drop the cabin temp from say 130 F (parking) to maybe 95 F (it is hot in SC).
Then the air-conditioner churns away 100%of the time and in re-circ mode because Mazda Air conditioners are so-so in the CX-5. Maybe it's the HFO-1234yf; I don't know. I mean it works but takes some time to cool down then does a good job. Even if it cost me 3 MPG (unlikely) that is only like an extra $4 a week, and I would rather be cool.
It is hot in SC
Then the air-conditioner churns away 100%of the time and in re-circ mode because Mazda Air conditioners are so-so in the CX-5. Maybe it's the HFO-1234yf; I don't know. I mean it works but takes some time to cool down then does a good job. Even if it cost me 3 MPG (unlikely) that is only like an extra $4 a week, and I would rather be cool.
It is hot in SC
4wd
$50 site donor 2026
I roll down one window driving through the Beer Barn 
I don’t like wind noise so I keep them up at high speeds. To note some vehicles allow you to lower the windows by holding the unlock button down or..? Some VW, Audi, Honda, Ford… models
edyvw
$50 site donor 2026
Depends. European vehicles, all I think, have that feature in Europe. Here they remove it (decode it) bcs. NHTSA etc.
You just basically have to code it again. I coded in my BMW:
hold unlock 0.5sec: starts opening windows, if held long enough it will open sunroof.
Hold lock 0.5sec: rolls up everything.
Lock: folds mirrors.
Unlock: open mirrors.
You can adjust how long you have to hold button. You can roll down or up with single press, hold 0.5sec, 1 sec etc.
You can set light on/off when unlocking etc, etc.
Everything is already written in DME, you just need appropriate OBD like ProTool ($100 Android based. Basically “translated BMW diagnostic program for regular folks to use) or BMW INPA/ISTA (free to download). FoxWell etc. won’t work.
My Tesla will have a message in the energy usage app telling me I’m losing efficiency if I drive with the windows down on the highway.
Windows 11? /s
Patman
Staff member
This happens for me even when I’m going 50-70 mph
I take the doors and top off. Lighter weight=better mileage. Wait….this isn’t the Jeep thread….
My 86 Plymouth Turismo Duster got way better mileage with the windows down than up with the AC on. I’m glad things have improved since the 80’s.
My 86 Plymouth Turismo Duster got way better mileage with the windows down than up with the AC on. I’m glad things have improved since the 80’s.
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