I hope I don't get flamed for this...

I heard that driving with your windows up greatly increases your aero dynamics and even improves gas mileage. Anyone agree with this?

Also, I was curious about having your sunroof/moonroof tilted open...I always drive with it open (tilted). Would this effect Aero Dynamics or create any drag? If it did would it even be noticeable? I doubt anyone has a windtunnel to prove these theories, but maybe some one knows something I don't.

Am I crazy for asking this question?

 

omg...
what makes you think lowering the windows will increase the aerodynamic
efficiency of the car (lower the drag?..)

but well, back to the sunroof problem, when u tilt the sunroof up, it will act "kind of" like a roof spoiler. Hence, the aerodynamic characteristic of the
car would be changed...

 

No...having the windows UP (not down) would increase aero dynamics

I know tilting the moonroof might create a bit of a spoiler effect. However, on the same token, would a vacuum be created by letting air into the cabin from the top??

 

When you guys take your cars to the track do you close all windows?

Do some drivers have a preference on one or the other?

 

godmans, read the post before responding. he referenced having the windows up, not down, would increase aerodynamics. And he's right. There is significant drag with windows down. For highway driving, MPG is actually lower with windows down and AC off, than with windows up and AC on.

As for the moonroof, my guess would be that having the roof tilted would not matter a whole lot. Open probably much more. My question is, who gives a ****?

At the track, you should always have all windows closed.

 

In theory, having the sunroof tilted up would most definetly affect aerodynamics. The whole idea behind good aerodynamics is controlling the smooth flow of wind. Anything that causes that smooth flow to be disrupted will increase aerodynamic drag (that's why a golf ball has dimples). Tilting the sunroof up will most likely cause a disruption in the airflow over the top of the car. This turbulence will increase drag. The question is how much increased drag? And is it enough to make a difference in fuel economy?

 

I've tested this on my driving.... Driving with windows up and using AC or driving with windows down and NOT using AC. I did not get technical with this however, the 2 tests should be relatively consistent.

For one work week I drove to work and back with windows up using the AC at a consistent temperative. For another week I drove to work and back with windows down using no AC. The weather was similar, high 80s/low 90s, and traffic was similar, combination of regular highway/interstate and some bumper to bumper.

Although I didn't get technical it appears I got more MPGs with windows down, no AC. I base this off the fact that I got about 4 days with AC, 5 days without.

None-the-less... Windows are down most the time for me. As long as I can bear the Atlanta heat.

 

ok mike, first of all, my bad that i misunderstood your post. Secondly,
regarding the track rules, i believe the common practice for many tracks
that i have gone is to throw all your front windows (down) and leave
your sunroof closed.

For titling the moonroof, by my technical experiences on fluid and flow
dynamics, it has little effect on the overall aerodynamic characteristic of
the car (unless if you are going at the speed of a sub sonic jet).

Cheers,

 

Mythbusters on TV did a test to see which is more efficient - windows down or AC. They used two identical Ford Explorers on an oval track and tested at highway speeds. The windows up, AC Ford won by a huge margin. However, at traffic speeds, I would think windows down would have the edge because you are frequently at a stop and idling.

 

+1.
that's my understanding too.

MikeyMike,
you won't get flamed for asking this type of Question or any other reasonable question, No worries. T
These days, with high fuel prices, answers to these type of questions is very important.
I personally hope that everyone takes an interest in saving fuel and doing their part.

The sunroof answer I can only guess and say that tilting it will have a very minor negative effect on fuel consumption. A big benefit of having it tilted would be that air movement may be sufficient to avoid A/C use. Obviously if it's 95 degrees out, the s/roof will be closed along with all other windows, and the A/C will do its thing.

As has been said, having the windows down, will have a serious effect on mileage.......more than with them up with the A/C on, especially Econ A/C.

No you're not "crazy", indeed, kudos for caring. If everyone did, then consumption would drop as would these high prices.

C.

 

I just read about that on a gas saving review on MSN