List of aero mods you can do to your vehicle

[MetroMPG]

Feel free to reply with links & examples. I'll update this top post.

Note: some of these mods may make your car less safe and/or illegal (e.g. mirror/wiper deletion). Don't blame us if you do something silly and get caught or crash into a tree in the rain.

Deletions:
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- Roof racks (OEM as well as aftermarket)

- mud flaps

- raised wing type rear spoilers

- Side mirror delete (MetroMPG; Peakster's video test)
(with optional inside convex mirror replacement; or for less extreme, install mirror(s) you can fold back)

- Radio antenna

- shaved excrescences (badges, door handles, rain gutters)

- windshield wiper delete (front & rear)

Replacement parts:
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- smooth wheel covers

- narrower tires

- upgrade from "bucket" style to aero headlamp assemblies

- swap to a more aerodynamic bumper cover style (Metro)

Modifications/fabrication:
----------------------------

- fabricate lexan/plastic covers over "bucket" style headlight treatments (Coyote X's Metro)

- grill block (Metro, Dodge Caravan, CRX)

- tire spats, or fully contoured deflectors

- boat-tailing behind tires (Aerocivic)

- belly pan / under tray (1st gen Prius)

- rear wheel skirts (Metro, Civic)

- front wheel skirts (Daihatsu Mira)

- if no front wheel skirts: softened/radiused aft edge of front wheel arches (see: VW 1L car, Solectria Sunrise, Honda Insight, GM EV1)

- ... and/or gap fillers to minimize the space between the exposed tire & wheel arch (see Audi A2, Toyota Prius 2 for examples of cars with mimimal tire/arch gaps)

- reduced ride height - 3 inches is often quoted as optimal (CRX)

- taped/sealed panel gaps (or siliconed & razor cut)

- partial kammback (Metro), or,

- fulll boat tail addition (Aerocivic)

- pickup trucks: partial (rear) tonneau cover at a minimum, full tonneau, or complete aero shell (boattailed cap)

- radical frontal area reduction (e.g. tandem greenhouse)

- decreased (or is it "increased" - you know what I mean) windshield angle (e.g. addition of external clear "visor"), and/or increased hood angle

- increased radii at the front-to-hood & front-to-sides of the vehicle

- front air dam (as low as the lowest underbody components, possibly lower depending on the vehicle)

[Big Dave]

Another idea. Gap seals. Outfits that make aero mods for light planes are big on gap seals. Most aircraft panels are faired or at least fishscaled, but the flaps, ailerons and vertical stabilizer have gaps. They claim increased speed at level power settings.

Those clearly do work on 170 knot (200 MPH) aircraft but they may not be as effective for 70 MPH ground vehicles unless you have egregious gaps. The cab-to-bed gap on some pickups get overly large.

[JerkOfAllTrades]

Originally Posted by Big Dave

Another idea. Gap seals. Outfits that make aero mods for light planes are big on gap seals. Most aircraft panels are faired or at least fishscaled, but the flaps, ailerons and vertical stabilizer have gaps. They claim increased speed at level power settings.

Those clearly do work on 170 knot (200 MPH) aircraft but they may not be as effective for 70 MPH ground vehicles unless you have egregious gaps. The cab-to-bed gap on some pickups get overly large.

Hmmm, some blue painters tape and some testing could prove this rather quickly. Unfortunately I'm not in a position to try this out at the moment however, I'm willing to give this a go sometime this coming summer.

I should have some repairs and a good baseline for my car by then.

[Stan]

I know we have good data for some of these techniques, but has anyone measured (a-b-a) the effect for each of them? I am especially interested in rear wheel covers and smooth hubcaps, as these might be something SWMBO might go for.

[AndrewJ]

Stan, you just might be in luck.
I've been thinking that I should go get my testin' on tomorrow or Friday... Some good ol' A-B-A on the test hill, been thinking about throwing in a C-D-E as well.

I just might get motivated enough to do it.

[MetroMPG]

Darn you Californians and your good testing weather.

I've attempted to test rear skirts 3 times on 3 different vehicles: details here

In all cases, the tests were less than perfect, despite 2 of the 3 being A-B-A style (I concluded based on the 2 sets of A data that the drivetrain temps hadn't stablized).

Results were between 0.6% MPG improvement to 2.7%, with the largest impact seen on the Metro (which I think is due to the design & placement of the wheel arch).

[Fuzzy]

Originally Posted by Big Dave

Another idea. Gap seals. Outfits that make aero mods for light planes are big on gap seals. Most aircraft panels are faired or at least fishscaled, but the flaps, ailerons and vertical stabilizer have gaps. They claim increased speed at level power settings.

Those clearly do work on 170 knot (200 MPH) aircraft but they may not be as effective for 70 MPH ground vehicles unless you have egregious gaps. The cab-to-bed gap on some pickups get overly large.

Sailplane pilots use gap tape quite a bit too (ailerons, flaps, and wing/fuselage connections). Blue Painters tape would be okay, though you'd want to make sure that it doesn't 'sag' into the gap; and that there are no wrinkles/ripples.

[brucepick]

MetroMPG - You mentioned an air dam in the original post.

Can you (or trebuchet03 or anyone else for that matter) expand on that some, provide some detail on why it works?

I've seen some posts on non-FE sites, saying that an air dam will increase drag and reduce FE. I say that's likely true if the air dam is designed to create downforce. I'm pretty convinced of the FE value of an air dam that's designed for FE, especially if a belly pan is included to seal off the gap. But it would be good to see some more detailed analysis.

Thanks in advance.

[virg]

I wonder about a bracket up front with a ball or bulb leading the way, like that bulbuous thing on the hull of a ship that parts water. Make it a sliding-adjustable arrangement with the bulb leading the grille.

[donee]

Hi Virg,

I am no expert, but the bow bulb on a ship has to do with the interface between water and air. The bulb lifts the water ahead of the ship, which then falls away from the above water bow. Apparently its takes less work to lift the water than to push it aside (air is more compressible than water, and one is pushing against air when lifting the bow water).

On a car, or submarine, or airplane there is no such interface involved, and hence no bulbs.

[mpgvalues]

Just so you know I've been browsing through this site and I think some of things you guys try are a little loopy. Dont get me wrong, some are ingenious, practical, heck it even looks like fun. But yeah, a little odd Keep going I say.

[Achtung]

Originally Posted by donee

the bow bulb on a ship has to do with the interface between water and air. The bulb lifts the water ahead of the ship, which then falls away from the above water bow. Apparently its takes less work to lift the water than to push it aside (air is more compressible than water, and one is pushing against air when lifting the bow water).

I always wondered how those bulbs made it easier for the ship to push through the water... that explanation makes alot of sense! I never thought of it that way. Thanks for that! Kinda gave me a eureka moment there...

[aerohead]

Originally Posted by virg

I wonder about a bracket up front with a ball or bulb leading the way, like that bulbuous thing on the hull of a ship that parts water. Make it a sliding-adjustable arrangement with the bulb leading the grille.

The History Channel had a program about the Japanese Imperial Navy's flagship,Yamato.The project was very classified,and the nose of the ship was top-secret,and a hydrodynamic coup for the day,and has found its way into the U.S.Navy (USS Ronald Reagan),and Soviet Navy ships,as well as merchant vessels.According to the narrator on the TV program,the bulb created a counter bow-wake underwater,which cancelled the bowwake above waterline.Sorry! This is a little deep for me.A fellow tried this at Bonneville on a streamliner.Best I can tell,it failed to be effective.

[Randy_the_Hack]

Fellas...

It would be nice to have a sticky out here that broke things out in a quick reference manner:

• Car mods
  • Prioritized list of aero mods
• Truck mods
  • Prioritized list of mods

Realizing that various mods deliver different percentages of improvements per vehicle, these might be somewhat general. For example, with a truck, the likely top few mods might be a) lowering the truck, b) less aggressive tire tread and size, c) aero bed cover, etc.

So... unless there is some data out there that indicates smooth wheel covers are a huge saver, I would expect to see these generally at the lower end of the spectrum. I realize that this might be too precise, so grouping in general categories of top mods, middle mods, and everything else, might suffice.

Breaking this out by cars v/s trucks would be quite helpful...

Just my $0.02...

[aerohead]

Originally Posted by Randy_the_Hack

Fellas...

It would be nice to have a sticky out here that broke things out in a quick reference manner:

• Car mods
  • Prioritized list of aero mods
• Truck mods
  • Prioritized list of mods

Realizing that various mods deliver different percentages of improvements per vehicle, these might be somewhat general. For example, with a truck, the likely top few mods might be a) lowering the truck, b) less aggressive tire tread and size, c) aero bed cover, etc.

So... unless there is some data out there that indicates smooth wheel covers are a huge saver, I would expect to see these generally at the lower end of the spectrum. I realize that this might be too precise, so grouping in general categories of top mods, middle mods, and everything else, might suffice.

Breaking this out by cars v/s trucks would be quite helpful...

Just my $0.02...

Randy,you asked for a very useful sticky.And while its a daunting task,I'm assembling whatever material I have and will post as I can.In the meantime I wanted to share info on some papers that basically answer your questions if you can access them.SAE Paper No. 649A "Aerodynamics for Body Engineers" by Kelly and Holcombe,1963,and SAE Paper No. 649B "The Body Engineer's Role in Automotive Aerodynamics" by Walter H. Korff,January 1963.Between the two papers,the authors lay out where all the energy is going,and in the second paper,especially,Korff lays out a recipe for Cd 0.21 cars (remember this is 1963!) and quantifies the difference between drag contributions for all body elements.SAE Paper No. 690189 "A Method of Estimating Drag Coefficients" by R.G.S.White,also lays out a cookbook approach to low drag cars,breaking a car's body into 9 categories.From the tables,one can deduce drag potential ( and elimination) within each of the 9 categories.Last paper is SAE No.760185 "The Optimization of Body Details-A Method for Reducing the Aerodynamic Drag of Road Vehicles" by Hucho,Janssen,and Emmelmann,all from Volkswagenwerk AG.Again,the paper as in the later book,breaks down a vehicles drag components and attaches numerical values to each and shows potential gains should each be realized.If you can get a copy of Hucho's book it will have all the data you seek.

[i_am_socket]

Perhaps some before/after thumbnails of the particular mods to get an idea of what would/wouldn't work for your vehicle could be included along with the links?

[aerohead]

Originally Posted by i_am_socket

Perhaps some before/after thumbnails of the particular mods to get an idea of what would/wouldn't work for your vehicle could be included along with the links?

Actually,Hucho's book has everything,and before and after for everything,with a quantitative assessment of everything done.Its quite a goldmine.

[Randy_the_Hack]

Originally Posted by aerohead

Actually,Hucho's book has everything,and before and after for everything,with a quantitative assessment of everything done.Its quite a goldmine.

Yeah but when I looked for that book, the cheapest copy I could find was something like $185, and it was in German, IIRC. Ich spreche nicht oder lese Deutschen.

[aerohead]

Originally Posted by Randy_the_Hack

Yeah but when I looked for that book, the cheapest copy I could find was something like $185, and it was in German, IIRC. Ich spreche nicht oder lese Deutschen.

Randy,I was surprised when I read your post,however,perhaps not as surprised as you,when you saw that price! Sounds like gouging to me.I paid $80 back in '90.I saw where members were picking them off Amazon or ebay for $100.00.If it weren't in Deutsch I'd say go for it.For what it will give you its a bargain,but not with the hassle of translation.I'm pulling some materials together for those who just don't have access but it will take more time.

[i_am_socket]

For the un-enlightened among us: what is this "Hucho's book"?