Honda Insight Forum banner

1 - 20 of 27 Posts

·
Registered
Joined
·
351 Posts
Discussion Starter #1
I’m curious to know if anyone has any observations concerning MPG and 2 aerodynamic modifications frequently made on our insights; i.e.: adding front license plates and opening windows. I realize that both of these factors are extremely minor and that their effects are speed related, but it surprises me that I can find no mention of them here (maybe I have not read each thread carefully enough). It seems to me that an open window could affect MPG almost as much as a missing wheel skirt.
Just wondering…
 

·
Registered
Joined
·
700 Posts
Yeah, but stick your hand out in the breeze to do the "wave" (you know what I mean) will cost you 10%... Dog's head: 8% (but 12% with tongue unfurled)...:wink:

Seriously tho...

I would think that adding frontal surface area would have the biggest impact on the overall drag, which none of the above do.

My intuition fueld by limited knowledge of aerodynamics (didn't quite finish that AE degree before getting sidetracked...) tells me that the windows down would not interrupt the flow very much, eh?
 

·
Registered
Joined
·
351 Posts
Discussion Starter #4
I agree, my intuition would say that windows should not matter that much, certainly not as much as A/C. But then again everyone seems to keep their skirts on. (Modesty?)

How about that flat front license plate? Since here in Ca. we’re supposed to have one I’ve thought about taking the front bracket off and bending the plate a little to make it rounder.
 

·
Premium Member
Joined
·
1,658 Posts
In the dim and distant past, I remember reading that driving a standard car with the windows open reduces your MPG by 4%.
 

·
Premium Member
Joined
·
830 Posts
Hi,

I would not think that the license plat would have an effect. It does not add to frontal area (the bumpper and all of the car is behind) and it is placed where the air is pressured and not flowing horizontally. Meaning that with or without, the air needs to go either up or down.

For the window, I have tried that in the summer and it did not have an apparent effect on the MPG display.
 

·
Registered
Joined
·
700 Posts
dan said:
I agree, my intuition would say that windows should not matter that much, certainly not as much as A/C. But then again everyone seems to keep their skirts on. (Modesty?)

How about that flat front license plate? Since here in Ca. we’re supposed to have one I’ve thought about taking the front bracket off and bending the plate a little to make it rounder.
Have you seen one with the skirts off? If so, then you understand why they stay on...not a pretty sight.

I don't see any harm in "smoothing' the blunt plate a bit. Wouldn't help in the big picture, but would seem more fitting in its application....
 

·
Premium Member
Joined
·
830 Posts
Hi,

I would say that just for the looks, it is quite better looking without the plate holder.
 

·
Registered
Joined
·
228 Posts
One thing I've noticed with all of our recent rain is that at speed, with the rain coming straight down, the side windows never get a drop on them. This must say something about how the air travels around the car and that having the windows down shouldn't make much of a difference.

Anyone brave enough to drive in the rain with the windows down and see what happens? 8)
 

·
Registered
Joined
·
1,123 Posts
In most regular cars driving at highway speeds, it's more fuel efficient to use the A/C then drive with the windows open.
Keeping the windows closed is very important for high speed aerodynamics.
 
G

·
Guest
Joined
·
0 Posts
Hi Guillermo:
Guillermo said:
In most regular cars driving at highway speeds, it's more fuel efficient to use the A/C then drive with the windows open.
Keeping the windows closed is very important for high speed aerodynamics.
___I would tend to agree with that statement in every other automobile I have ever owned. Other then for the Insight that is. When you roll down the Insight’s windows, it doesn’t seem to have the wild buffeting that most cars have. Even the relatively clean 03 Toyota Corolla w/ a Cd of .29 has some pretty wild wind blowing around in it with the windows down at hwy speeds. I have only had the Insight’s windows down when clearing heat twice now up to ~ 30 mph and there just wasn’t a feeling that much was coming in or out. I guess I will know more when it starts to really warm up around here in the not to distant future.

___Good Luck

___Wayne R. Gerdes
 

·
Premium Member
Joined
·
394 Posts
Hi Wayne; I believe Guillermo is correct on this one. I have done considerable experimentation and aerodynamic calculations (similar to evaluating certain aspects of my airplane's performance). I estimate that in calm winds, travelling above 53 mph, with both windows fully down, my Insight loses more mpg than it would if the a/c were on and the windows up. At low speeds in the city, there is minimal affect. But with both windows fully down, travelling 70 mph for example, there is a tremendous amount of induced drag (different than parasite drag, i.e., a your hand sticking outside the car). Billy......
 
G

·
Guest
Joined
·
0 Posts
Hi Billy:

___Thanks for the heads up and long time no hear! In the Corolla and MDX, this is definitely true but I wasn’t 100% sure about the Insight? About how many mpg do you lose with the A/C on vs. off in 78 - 90 degree F temperatures? When it’s hot, I like my A/C so I suspect it will be on a lot unfortunately :(

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email:lcnq4rfj][email protected][/email:lcnq4rfj]
 

·
Premium Member
Joined
·
891 Posts
xcel said:
there just wasn’t a feeling that much was coming in or out.
If no air blows into the vehicle when you have the windows down, then there will be no additional drag. If air does come in, then the car will experience higher pressure drag (referred to as induced drag by Billy) forces because now there will be low pressure on the forward part
of the cockpit (interior windshield, dash) and high pressure on the rear windshield glass.
 

·
Premium Member
Joined
·
394 Posts
Hi Wayne; There are several variables to consider. But with your driving style and high mpg, I would estimate that on flat ground, constant 60 mph
with 78 to 90 degree ambient temp, your mpg would drop from about 82 to about 66 during the time the a/c compressor is actually on. However, you can toggle the button and the compressor will only be on, say, one minute out of every 4 and maintain a comfortable cabin. Rickly can advise; he is very good at doing this.

By the way Wayne, I enjoy reading your posts. Your knowledge, interest and enthusiasm is evident. Thanks, Billy......
 

·
Registered
Joined
·
106 Posts
I installed a clear plate cover with a slightly rounded face and rounded corners. The plate looked very flat to me in the front of the nice insight nose. I think it must help slightly, no idea how much, but it definately looks better. I hate walmart, but it was the only place I could find one. BELL clear polycarbonate. I had to get longer screws for it and ended up using 0.75" #14 sheet metal screws.

Any idea how much it would help to take off the antenna? (unscrew i mean)
 

·
Registered
Joined
·
700 Posts
sunhunter said:
Any idea how much it would help to take off the antenna? (unscrew i mean)
I'm guessing about 0.028% reduction in Cd, plus or minus.

Probably would offset the increased drag of the new front license plate... :wink:
 

·
Registered
Joined
·
351 Posts
Discussion Starter #18
Thanks Billy! I figured there must be someone like you out there. I wonder if your experiments included opening only one window, and how that changed your observations?
A rounded plate cover. I thought the high speed crowd would have an answer to the flat plate issue, (even if it doesn’t really make a difference). But I never would have thought to look in wal-mart, and I still don’t have any idea if it does make a difference.
While I’m thinking about it does anyone know why many older (80’s, 90’s) style headlights have the little “pimples” that protrude from the front of the glass? I had always suspected that they might have some aerodynamic effect but I have no Idea.
 

·
Registered
Joined
·
2,448 Posts
I don't proclaim to be any sort of AC use expert, but I've found the minimal comfortable level you can run the AC at while using the least possible is ac on econ 80 with the fan on 3/4 or full. This is what I used to use, but after having evident battery deterioration after a few summers I've decided to burn some gas and save the car. On hot days I will run the ac on auto until the car cools down sufficiently, then switch over to econ.

Now since we're on the topic of aerodynamics here are some other thoughts for the theoretical Insight EV conversion in the back of my head.

Finish it off, get creative with some fiberglass and close the large opening in the front bumper. Leave the small one for sufficient air flow for AC still, even make it like a EV1 bumper. Next, shave everything. Replace side mirrors with cameras. Find someone really good at alluminum welding and delete the antenna. Make the whole roof the new raido antenna. Shave the door handles, make them work by remote actuators. Do a rear wiper delete, this has already been done.

I don't know if there's much if you could do for the under side, though I suppose you could go as far as making a custom belly pan and get perfect smoothness underneath.
 

·
Registered
Joined
·
1,819 Posts
I've done some practical experiments that suggest there's little or no difference in drag with the windows open or closed. There's a long (about 10 miles) downgrade that I frequently drive in the summer. It's steep enough that I maintain highway speed without any throttle at all, but need to brake only occasionally, on a couple of curves. Depending on the temperature, I may drive with windows open, part open, or closed, but I've never noticed any difference in speed.
 
1 - 20 of 27 Posts
Top