Reducing aerodynamic drag

[Matt Timion]

Another easy way to increase fuel economy is to reduce aerodynamic drag. Engineers have been doing this for years, but sometimes they just forget to do it, or don't do it well enough.

I was checking out our newest member, Ernie Rogers, and I viewed his website: www.best-mpg.com

So Ernie reduced the aerodynamic drag of his VW Bug and has increased fuel economy 5-8%!

Check it out:




Hopefully Ernie can be a big help for us here. If at all possible Ernie, can you write an article for us to go into the "gas saving tips" about aerodynamic drag? It would also be good to include your own experiences. If you don't have the time, mind if I use you as an example (and perhaps use some of the content on your site) for such an article?

Glad to have you aboard, and glad to have another member from Salt Lake City!

[SVOboy]

I just posted about his damn fin, you foojin. You should prolly delete that now or move it over of something.

[dfoxengr]

how about the lowered truck tailgate? would adding a foil to that when lowered increase aero more than just lowering it?

also would fender flares help get drag away from going into the wheel wells?

and lastly(not a question)...anything covering up bump and valleys in your car such as the windsield wiper "ditch" and all the openings on the grill, and the rough underbody will help, such as the forementioned chin spoilers, as well as rear and front splitters....

[Ernie Rogers]

This will probably surprise many-- I think it's hard to reduce drag. Some kinds of cars make it easy. The Beetle was badly designed in the first place, at least regarding drag. 85% of the drag of a vehicle occurs at the back-- the fastback shape of the Beetle keeps the air flow attached at the back, and that causes the high drag: Cd = 0.38. I just fixed the problem by redirecting the airflow backward, forcing it to separate from the car. That's the simple explanation.

Pickup trucks have horrible drag, about 0.4 to 0.5. Again, the problem is fixable, and this is an opportunity for an inventor to develop a new product.

A well-designed car already has about a million bucks invested in drag reduction by the manufacturer. There are little things you can do, like rear wheel well covers /fender skirts. Any open pockets under the car should be covered. My Beetle has a lower engine cover that encloses the underside of the engine compartment. If you don't have one on your car, that would be a good place to start.

I think one of the best things people can do is to get efficient tires.

Ernie Rogers

[Matt Timion]

Originally Posted by Ernie Rogers

This will probably surprise many-- I think it's hard to reduce drag. Some kinds of cars make it easy. The Beetle was badly designed in the first place, at least regarding drag. 85% of the drag of a vehicle occurs at the back-- the fastback shape of the Beetle keeps the air flow attached at the back, and that causes the high drag: Cd = 0.38. I just fixed the problem by redirecting the airflow backward, forcing it to separate from the car. That's the simple explanation.

Pickup trucks have horrible drag, about 0.4 to 0.5. Again, the problem is fixable, and this is an opportunity for an inventor to develop a new product.

A well-designed car already has about a million bucks invested in drag reduction by the manufacturer. There are little things you can do, like rear wheel well covers /fender skirts. Any open pockets under the car should be covered. My Beetle has a lower engine cover that encloses the underside of the engine compartment. If you don't have one on your car, that would be a good place to start.

I think one of the best things people can do is to get efficient tires.

Ernie Rogers

I'm curious to know how much adding a front bumper lip will help with reducing drag. Some people install the "home depot" lip, which is just garden edging screwed onto your bumper. A $10 modifcation like that might help a little... or maybe not.

[SVOboy]

What I am wondering is for patching things up under the car to I just get under there and find the holes and cut our some plastic sheets (like solid types) and tape it the hell on there, or what?

[dfoxengr]

get creative. watch for high temp areas, and what youre poking holes in though.

[kickflipjr]

I was also thinking about puting on a home depot lip. will that help at all? I mught put one on sooner or later.

[dfoxengr]

it's possible. no way to know unless you get really consistent numbers, or take it to a tunnel...

[Jonathan_ED3]

Originally Posted by Matt Timion

I'm curious to know how much adding a front bumper lip will help with reducing drag. Some people install the "home depot" lip, which is just garden edging screwed onto your bumper. A $10 modifcation like that might help a little... or maybe not.

After I lowered my previous Civic sedan and installed an Integra front lip, and had my alignment corrected for everything including camber, my average MPG went up 2-3miles on every tank.

[Matt Timion]

Originally Posted by Jonathan_ED3

After I lowered my previous Civic sedan and installed an Integra front lip, and had my alignment corrected for everything including camber, my average MPG went up 2-3miles on every tank.

How much of this do you think is the lowering and how much is the lip? If I don't lower it and just put on an integra front lip (what years BTW?) do you think I'll see an increase?

[SVOboy]

Integra lip would be hot. I think it'd be about 50/50, because neither really have much weight over the other, since they both just keep air out from under the car. It might also be that it is a combination of the two the goes up by some function not just linear.

[dfoxengr]

im sure a lot of it was due to your previously faulty camber/caster etc.

i bet youll maybe get .1 mpg increase with a lip only.