Hi!, I just got my 09 Sport Fit today, so I'm new to the Fit scene (although my last car was an 02 Civic). I really choose the Fit for the cargo room, but getting the best mileage I can also seems like a worthwhile goal.

I live in Texas, so I have to use the A/C sometimes. But in the mornings and evenings, I really prefer to just roll the windows down and enjoy the breeze. I know that's not ideal for the aerodynamics, but I'm wondering which is better for fuel efficiency? Open windows or A/C? How much does the extra wind drag of open windows affect mpg? Has anyone road tested this, or seen any reliable figures?


Thanks

 

I live in South Fla and don't use A/C unless I have someone in the car that insists. Without question, windows are better for FE, but here's so pointers. At low speeds (stopped to say 40mph) when hot open all 4 if needed.
From 40 to 50 back ones 100% up fronts down.
At 55 or above (if you want to drive like a nut), back still up and fronts no more than 1/2 down.

I find a better wind in face with backs up at speed.
Soon as I slow down for traffic or a light I feel the heat and roll them all down hoping for a side breeze.

 

Actually, around town I usually roll the rear windows down so my canine copilot can stick her nose out. But following your guidelines sounds like a more systematic method that would keep the wind drag to a minimum.

Thanks

 

Open windows for me hands down. I can maintain 40mpg in stop and go traffic. 65 mph max.

 

I remember cars in the 1950s with vent windows, floor and side vents, under the seat heaters and two heaters in the dash with individual controls for driver and passenger. Side mount vents flowed enough air to offset the wind coming through the windows and made for a very comfortable ride from 30 MPH on up making an AC unnecessary except in stop and go city driving.... It would be nice if these features were offered on today's cars..... Sun roofs and vent visors just aren't as effective and hamper fuel mileage more than the old time stuff.

 

too damn hot to not use AC in texas...lol

 

85 degrees in Houston is worse than 112 on the High Plains. This has been the coolest weather for June, that I've seen in Texas in 21 years.... The hottest it has gotten here was 97 and it was only 95 today..... It feels more like April to me.... Houston though is worse than Vietnam and just as dangerous if you are driving a Fit.

 

IIRC, mythbusters did an episode where they tested this out. I think it was something like above 50MPH, it's not any different. Below 50, of course the windows win out. Someone correct me if I'm wrong.

And although they weren't using the Fit or a Honda, I'd think it would apply even more to 4-cyl Honda's since the extra drag would affect our torqueless motors more.

I know what it's like living in a humid place (grew up in the South). There is no way I'd go A/C-less during the summer.

 

Whenever they get around to using the traction drive CVT on crank pulleys, there won't be as much power loss from belt driven accessories A/C use won't hurt performance as much and water pumps, alternators and A/C compressors will not have to be built as heavy to handle high RPM.

 

I know its fun to drive with the windows down but i would not recommend it for your ears sake. Driving witht he windows down is more damaging for your ears than being at a loud concert, you will not notice it right away because it attacks your lower frequencies but the extra 2$ pr fill that you spend on AC will save your hearing when your 70.

 

Lots of college theses have been done on this subject; the agreement is in town at low speeds A/C uses more gas; at highway speeds (50 mph or more) the extra wind resistance fromopen windows uses more gas. And when I lived in TX I had to use A/C all the time.

 

couldn't agree more. plus, if you like to listen to music, you might feel more inclined to turn it up louder to accommodate for the wind noise

 

its been around 85F here during the hottest times of the day. I usually always roll with the windows down, unless I really don't feel like getting sweaty. I find that I'm fine with all windows down at 70mph unless I get near an 18wheeler, then the car starts getting pushed around by the wind until i roll up all the windows about 2/3.

As far as A/C vs Windows at Highway speeds, I haven't really noticed a difference but I don't have a scangauge. When I do roll with the A/C I never push it above 2 as far as blower speed and I leave it on outside air until I fill up the car with enough cold air to start the closed loop and not have to recycle hot air.

EDIT//
Sometimes I wonder about this since I like to take care of my hearing (do alot of hobby music stuff) But I'm sure if I got any ear damage it would have been years ago when my brother had a truck with no A/C and windows down was the only way to roll. (of course if you have the windows up more then less wind is directly in your ears. So that would be the good thing to do if you wanna be better safe than sorry.

 

Tip:

Q: Which method for keeping cool during the summer is better for fuel efficiency—air conditioning or opening the windows? And what role does a sunroof play?
—Wilson Leeson, Portland, Ore.A: At highway speeds you are best off closing the windows and sunroof, because opening them often causes enough drag to offset any savings from turning off the air conditioner. When driving slowly around town, where drag is less of a factor, keeping windows and sunroofs open typically uses less fuel than running the AC.
Of course, the most efficient car is one with the AC off and the windows and sunroof closed. Using the car’s vents might circulate enough air to keep you comfortable on days when the weather isn’t particularly hot or when the car’s interior hasn’t been preheated by sitting in the sun.
Is Running Your Car’s Air Conditioning Fuel-Efficient? - WSJ.com


What it really means...
Get a white car. Block as much sun as possible from the interior of the car to keep it from heating up excessively. Park in the shade. Park under a tree. Park in a parking garage. Vent that nasty hot air out as soon as you get in the car by opening the windows.



It's not an all or nothing proposal. You CAN turn on the a/c to help cool the interior off, and then turn the fan to low, switch back to fresh air (non-a/c).



Most folks don't have a side of beef in the cargo area to keep chilled. Keep the temperature bearable. It doesn't have to be perfect or ideal. It just has to help protect against heat stroke.

 

Drive under 30 mph with windows open and over 30 with windows closed to minmize air resistance.

 

I read your post really fast, and I thought it said:

over 30 with windows closed to minimize ear resistance

Because people were talking about ears and hearing.

I still think they should have those little back windows open, power close at shut-off (like a sunroof does), and the open is a choice.

I think that would be great ventilation for the entire vehicle, providing a large exit point (relatively speaking) for the incoming air on vent/fresh mode.

It could get a nice breeze going over the passengers, but would be far less drag, I'm sure, than opening any side windows. The back window could pop out at an angle with the open part towards the back of the car.

Like in mini-vans and some SUVs.

Posted about this idea over here first:
https://www.fitfreak.net/forums/tell...k-windows.html

What do you all think about that idea?

 

Its not letting the incoming air out the rear windows, its the air tubulence, or those swirling air currents that produce drag. no matter how the incoming air is balanced with exit the air sreams get more turbulent, or higher energy swirls, aka miniture tornados, that produce more resistance to the vehicle slipping thru the air.Above about 30 mph the drag from turbulence from open windows is reduced considerably by closing the windows.
Once over about 30 mph the energy producing more and higher energy swirls is much greater from open windows than from a closed window and unsmooth body. Hence less mpg.
PS sorry about the misspelled rears''. old fat fingers tend to do that.
cheers.

 

I'd like to learn more. Any links or sites you'd recommend?

It would seem that it would matter where the resistance occurred. Like if it happens at the very front of the car, it might mess up the entire aerodynamics.

But if it happened more towards the rear, that most of the car has already gone through the air and ...uh...hmmm. I guess that wouldn't work though, because boats are steered at the rear. The fact that the entire boat has already gone through water doesn't change the ability to steer it at the end.

Fluid dynamics for dummies, I need that link, I think, yes? Is that what I would be looking for? I can't do a search for something when I don't know what keywords will bring the desired results.

 

I'm in NH and I melt when it's above 80...

but I can drive with little or no heat at 40 degrees

 

Only aerodynamics textbooks and since I'm on vacation my texts aren't avalable. They are in your local library unless you are as far in the sticks as I. They aree rather complex and you end up with charts that estimate the increase in drag with unsmoothness in surfaces.
You ask if there is a difference whether the instbilites occur at the front or bacxk. very good question.
We measured total drag on our models or full size racers regardless where the instabilities occurred but only when direction was affected - steering problems that would result - did we really find if drag per se was important at the front or back. Since directional stability would likely lead to greater drag I would guess that drag at the front is much more imoportant to correct than that at the back.
Sure would be fun to check that even if I think its a foregone conclusion /. Perhaps we already know from firing arrows without feathers. The drag is then virtually all at the front and the range is severely shortened due to widely changing aerodynamics.