Question about Honda Civic vs. Civic hybrid Cd

[Vman455]

I was just looking through the list of drag coefficients in the wiki (like ya do...) and noticed something interesting: the 2001-05 Civic has a Cd of .36 while the 2003-05 Civic hybrid has a Cd of just .28! After looking closely at pictures of the hybrid, it seems the only body differences are:

1) an upper grill that looks to be mostly or completely solid
2) a small lip spoiler on the rear
3) a plastic tray under the engine compartment
4) redesigned external mirrors that have a smaller attachment point and allow air to flow between the body and mirror
5) .6" lower.

My question is: how is it possible that those (minor) differences are enough to lower the drag coefficient by .08 (more than 20%)? Am I not seeing something significant in the alterations to the hybrid model? Or is the number wrong?

The reason I ask is because, if it's correct, that low of a coefficient seems easy to attain--and it makes me wonder where my car is with what I've done to it so far....

[California98Civic]

Originally Posted by Vman455

I was just looking through the list of drag coefficients in the wiki (like ya do...) and noticed something interesting: the 2001-05 Civic has a Cd of .36 while the 2003-05 Civic hybrid has a Cd of just .28! After looking closely at pictures of the hybrid, it seems the only body differences are: 1) an upper grill that looks to be mostly or completely solid 2) a small lip spoiler on the rear 3) a plastic tray under the engine compartment 4) redesigned external mirrors that have a smaller attachment point and allow air to flow between the body and mirror 5) .6" lower. My question is: how is it possible that those (minor) differences are enough to lower the drag coefficient by .08 (more than 20%)? Am I not seeing something significant in the alterations to the hybrid model? Or is the number wrong?

The reason I ask is because, if it's correct, that low of a coefficient seems easy to attain--and it makes me wonder where my car is with what I've done to it so far....

I think you have the Cd for the hatch. I think the Cd for the coupe is .32 (but .28 is still a big improvement). The changes you describe sound like they might plausibly make such a .04 improvement, judging from what I have read and estimated for my own car after making somewhat similar changes. I have seen 0.36 as the figure for the coupe, but I think 0.32 is correct. The hatch is messier in terms of Cd.

[Cd]

I agree that has to be the Cd of the hatch.
The previous generation ( 92-95 ) actually had a better Cd for the hatch versus coupe ( .31 vs ..32 )
Amazing what a slight change in window angle can do to destroy a cars drag.

After seeing such big improvements from such little changes, it makes me wonder why car manufacturers brag about how many hundreds of hours they spend on a car to get the Cd down two or three counts.

[MetroMPG]

Looks to me like some other differences...

6) different front bumper / air dam [correction: they appear to be the same]
7) hybrid specific wheels
8) tire width?

[California98Civic]

Originally Posted by Cd

I agree that has to be the Cd of the hatch.
The previous generation ( 92-95 ) actually had a better Cd for the hatch versus coupe ( .31 vs ..32 )
Amazing what a slight change in window angle can do to destroy a cars drag.

After seeing such big improvements from such little changes, it makes me wonder why car manufacturers brag about how many hundreds of hours they spend on a car to get the Cd down two or three counts.

I saw that too, about the 92-95 Civics. The VX only came as a hatch, right? It had a small chin spolier, a backlight spoiler, only one outboard rear view mirror, and what else to achieve this .31 ... because as you say the back end should be worse than the coupe. Partial undertray? It's a curious fact.

[Vman455]

Originally Posted by MetroMPG

Looks to me like some other differences...

6) different front bumper / air dam
7) hybrid specific wheels
8) tire width?

It looks to me like the bumper/air dam is the same:

Hybrid:



Non-hybrid:



The wheels are 14" alloys specific to the hybrid, but they are the same size (and used the same tire size) as the 14" steel wheels on DXs and LXs. That seems a lot more believable that they got it down to .28 with those changes if it started at .32 rather than .36.

[MetroMPG]

I stand corrected. Thanks for that.

[LeanBurn]

I wish I could find out if a trunk lid spoiler on my corolla would make a difference compared to none...is there any way to computer simulate one..I wish I knew more about that sort of thing.