Biggest gains are at the back???

[COcyclist]

I have been pondering this for a while since observing that many posts about work done on the front of a vehicle get shot down in flames. (Picture Snoopy with smoke pouring out of his doghouse) Also, what I personally consider to be a couple of our leading authorities on this site (Aerocivic and Aerohead) have reshaped the fronts of their vehicles, as well as streamlining the back. Then I am reading a post from MetroMPG about the 2013 Chevy Malibu ECO aerodynamic tweaks and came across this:

10 counts: Underbody panels - two in the mid-body area under the floor pan on either side of the center tunnel, and two in the rear area covering the fuel tank and rear area on either side of the exhaust

10 counts: Rounded front corners - from the bottom of the fascia up through the headlamps - help air flow smoothly along the Malibu's body sides

10 counts: Tire deflectors positioned forward of the front tires act as "mini-air dams" to minimize wind disruptions

7 counts: The closed upper grille on select models pushes wind to the sides of the Malibu

7 counts: Outside rearview mirrors are specifically designed to deflect wind without "upsetting" the airflow

7 counts: Shutters in the lower grill opening on select models open and close automatically to maximize aerodynamic efficiency. This increases cooling airflow to the engine under certain conditions, such as under high-engine loads at low speeds, and reduces aerodynamic drag when extra cooling is not needed

5 counts: The front air dam redirects airflow to minimize aerodynamic disruptions

5 counts: The notch angle of the vehicle - the angle from the top of the rear glass to the trailing edge of the decklid - was optimized to reduce wind drag

2 counts: An integrated decklid spoiler incorporates a crisp, trailing edge that helps separate air from the rear of the Malibu.

The "rounded front corners" is 10 counts and the "decklid spoiler" is only 2 counts. Hmmm. I don't dispute the science that a full teardrop shape is essential for lowest drag in optimized vehicles. I just feel there may be some gains to be had at the front too. For many of us, a full boattail presents visibility, added length and parking problems. Should we as Ecomodders, do more work on the front before concluding that it is boattail or nothing?

[ChazInMT]

Keep in mind that if Chevy improved the rear to optimize it, it would have been 30 points or something. Most cars built today are falling in line with the "Fix the Rear" theory, so it is hard to deny. It's OK to question, but I wouldn't doubt it for long.

I saw a Chevy Sonic live in the wild for the first time the other day, very tapered both top & sides, very crisp trailing edges, just as we discuss in here.

[jimepting]

The car and the subject have already been discussed in some detail here:

GM describes 2013 Chevy Malibu ECO aerodynamic tweaks (Cd ~0.28)

That said, I still think that the experienced aerodynamicsist all argue that the greatest gains are at the back. Read Hucho. It is true that even Hucho argued that significant aero improvements could be had by attention to detail in the front, A pillars, mirrors, wheelwells, etc. but he showed his greatest experimental gains in the back.

The reason that the Malibu didn't achieve higher gains at the rear is that they didn't try very hard there. Significant gains at the rear require a sloping roofline(reduced rear headroom), tapered sides(reduced trunk space), gradual taper to rear glass(reduced visibility), extended length(weight and driving difficulties). The Malibu is slanted at the family cruiser market. In that context, it doesn't do too badly. Give the stodgy old GM some credit for at least concentrating on aero at last. Certainly they can do more.

[COcyclist]

Originally Posted by ChazInMT

Keep in mind that if Chevy improved the rear to optimize it, it would have been 30 points or something. Most cars built today are falling in line with the "Fix the Rear" theory, so it is hard to deny. It's OK to question, but I wouldn't doubt it for long.

I saw a Chevy Sonic live in the wild for the first time the other day, very tapered both top & sides, very crisp trailing edges, just as we discuss in here.

My wife's Audi A3 also has plan taper and a sloping roofline but the front end is like half a sphere. I think Chevy did optimize the Malibu within length, visibility and styling constraints. I want to boattail my hatchback but I have some of those same concerns. Are we ignoring modding the front of our vehicles just because "the biggest gains are at the back"?

[jimepting]

Originally Posted by COcyclist

Are we ignoring modding the front of our vehicles just because "the biggest gains are at the back"?

I think you may be right that we are ignoring the front too much, but it is natural that folks would go for the low hanging fruit first.

Like you, I've also been thinking about the front on my Gen1 Insight. I think the bumper could be replaced with a longer, better unit with a lower stagnation point and bottom feeding radiator intake. That coupled with a new hood allowing top exit of engine compartment air would be a slight improvement over the current setup, according to Hucho. Cabin air would have to come from some other location. But what I just outlined is as much work, or more, than making a good boat tail. See what I mean about the low hanging fruit?

[CigaR007]

The way I see it, by improving the front and middle sections of a vehicle, you are definitely helping the flow at the back. By concentrating on all aspects of the car, the gain at the back might even be better than expected, due to an optimized front end.

[fusion210]

10 counts is actually small. Well, small compared to rear end treatment!

Although it's argued that the biggest gains are at the rear, I think some of the lowest hanging fruit is sealing off any useless gaps in the front end and constricting airflow to the radiator.

[jimepting]

Originally Posted by fusion210

10 counts is actually small. Well, small compared to rear end treatment!

Although it's argued that the biggest gains are at the rear, I think some of the lowest hanging fruit is sealing off any useless gaps in the front end and constricting airflow to the radiator.

The first suggestion is kinda hard to evaluate, since most folks think it is rather small, but the second suggestion has been shown by various modders to improve fuel economy by 2-4%, definitely worth doing.

[KamperBob]

Between experts here and what I've read so far from Hucho and Hoerner there is interaction between front and rear. If (IF!) a given vehicle already has fully attached flow, THEN it seems that wake reduction provides more bang for the buck. If the front, top, sides and/or bottom are a mess producing detachment than wake reduction offers limited return. Perfect onset flow and attachment also tend to amplify base drag. So without good rear treatment, forebody work alone is limited. Everything matters.

Bullets make great projectiles. With enough brute force anything can be propelled. Successful gliders leverage eons of evolutionary wisdom of fish and birds.

[COcyclist]

Originally Posted by fusion210

Although it's argued that the biggest gains are at the rear, I think some of the lowest hanging fruit is sealing off any useless gaps in the front end and constricting airflow to the radiator.

This is an area of very high pressure air trying to force its way into every drag producing opening or gap.

Originally Posted by KamperBob

Between experts here and what I've read so far from Hucho and Hoerner there is interaction between front and rear. If (IF!) a given vehicle already has fully attached flow, THEN it seems that wake reduction provides more bang for the buck. If the front, top, sides and/or bottom are a mess producing detachment than wake reduction offers limited return.

I have been working from front to back on my vehicle, figuring I needed attached flow for the mods at the back to be effective.

Originally Posted by KamperBob

Perfect onset flow and attachment also tend to amplify base drag. So without good rear treatment, forebody work alone is limited. Everything matters.

Interesting, I don't have Hucho so I hadn't heard this before. So now that my front end and underside is smooth, I really need to get moving on my hitch mounted boattail/cargo carrier.