Long trip ahead, little prep time - best aero mod?

[NachtRitter]

Hi folks,

I have ~4,000 miles worth of driving coming up toward the end of April. Between now and then I have maybe one or two days free to improve the aero on my MKIV Jetta TDI. That means it has to be something relatively easy to do.

Currently I am getting ~60 to 65mpg cruising at ~60 to 65 mph on level ground with the TDI. I've done only minor aero mods (see grill block below), installed a taller 5th gear, and installed LRR tires. Just this past weekend, I installed a skid plate which seemed to help FE a little bit. And the stock wheel covers are relatively smooth already.

Grill block:


Wheel covers:


I will probably have time to do ONE of the following:

• Full under tray (probably not a one day project)
• Rear wheel skirts
• Home Depot Air Dam
• Smooth(er) wheel covers (probably won't gain much)
• Passenger mirror delete (probably won't gain much)

Your thoughts on which to do? Best aero mod for the effort?

[Sven7]

Undertray behind the rear axle to cover the spare tire area, and a partial kammback over the rear window.

[NachtRitter]

Good call on the undertray behind the rear axle... that'd be more achievable in a day than a full undertray.

Partial kammback I'm not so sure about... I'd looked at this thread closely: http://ecomodder.com/forum/showthrea...etta-5976.html. Seemed like the flow tests showed little benefit for a partial kammback. Or at best it was inconclusive.

[MetroMPG]

One or two days?

- Passenger mirror delete/replacement with interior convex is probably good for ~1-1.5%, and only takes a few minutes. I'd do it.

- Temp rear wheel skirts, duct taped on, good for another % or two: 30 minutes work

- Cowl block, if it's not going to be hot where you're driving (for ventilation, I mean)

- What about vertical spoilers ("trip strips") in the rear corner radii of the bumper cover/tail light area, a la Chevy Volt?

Has anyone done any testing on an air dam on that car? I'd be reluctant to throw one on, simply assuming that it's going to help.

[Cd]

This isn't an aeromod, but I assume that you have already planned the trip using Google Earth.
As you of course know, you can plan for changes in elevation ( to seek out flat roads versus hills, or roads with lots of turns. ) and population density ( more chance of a slow down in traffic )
You might even find a shortcut which saves both time and fuel.

[Cd]

I second leaving off the Kammback. Much to my surprise, this post : http://ecomodder.com/forum/showthrea...ibu-20326.html
Showed a possible increase in drag with a Kammback, and a sizable drop from a NASCAR style spoiler instead ! ( Aerodynamics are so unpredictable )

How much money are you willing to spend ? If you are willing to flip the cargo carrier the " right " way and add some coroplast to it, you could create a nice virtual boattail in a few hours time.


http://ecomodder.com/forum/showthrea...g-17911-5.html

And if you haven't already, of coarse cover the " parachute " under the rear bumper as everyone is suggesting.

[Cd]

Metro : I noticed one of the guys here at Ecomodder that came to your GreenGrandPrix had a hunter green Jetta TDI the same generation as this car. I remember it because it had a white ABS " catfish whiskers " style airdam which covers the wheels from the front, but is open in the middle, thereby decreasing frontal area.
I can't locate the image, but I know some of you guys will know the car.

[NachtRitter]

Originally Posted by MetroMPG

One or two days?

At least 2 days per direction... not in a major hurry

Originally Posted by MetroMPG

- Passenger mirror delete/replacement with interior convex is probably good for ~1-1.5%, and only takes a few minutes. I'd do it.

Good info; will look into that.

Originally Posted by MetroMPG

- Temp rear wheel skirts, duct taped on, good for another % or two: 30 minutes work

Have to translate that into 2 hours for me... at least!

Originally Posted by MetroMPG

- What about vertical spoilers ("trip strips") in the rear corner radii of the bumper cover/tail light area, a la Chevy Volt?

Hmmm... interesting... have to find some examples

Originally Posted by MetroMPG

Has anyone done any testing on an air dam on that car? I'd be reluctant to throw one on, simply assuming that it's going to help.

I figured something that goes down to the lowest point of the underbody and guides the air around the front tires... so not adding much frontal area...

Good inputs overall... thank you!

[NachtRitter]

Originally Posted by Cd

This isn't an aeromod, but I assume that you have already planned the trip using Google Earth.
As you of course know, you can plan for changes in elevation ( to seek out flat roads versus hills, or roads with lots of turns. ) and population density ( more chance of a slow down in traffic )
You might even find a shortcut which saves both time and fuel.

Haven't tried that actually... I did not know that I could use Google Earth to plan a trip that way... do you have a pointer?

[NachtRitter]

Originally Posted by Cd

How much money are you willing to spend ? If you are willing to flip the cargo carrier the " right " way and add some coroplast to it, you could create a nice virtual boattail in a few hours time.

Very cool idea, but that's a long term vs short term solution for me... I've always thought that using one of those hitch mounted cargo carriers would be a perfect platform for a removable boat-tail... but I know for sure I won't have the time to do that for this trip.