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Whoops 07-01-2008 12:05 PM

Mileage; Mythbuster?
 
All right, I would like some help.

My wife told me that she was watching a program where they claimed that washing your car and waxing it was something people should do, to get better gas mileage.

She said the program claimed that their is a 7% improvement in mileage, if you wash your car and keep it waxed.

I would not doubt that their might be a improvement, but their is no way that I can believe it would be 7%. I think the article was sponsored by Turtle Wax?

Does anyone have any ideas of what this figure might really be?

Shawn D. 07-01-2008 12:13 PM

Aside from removing large chunks of mud, washing and waxing will get you essentially nothing other than a psychological "improvement" in MPG. Cars are affected almost entirely by pressure drag, not friction drag. Washing and waxing does nothing for the former, but can be significant for the latter. Any improvement would probably be less than half a percent.

jesse.rizzo 07-01-2008 04:17 PM

In my aviation classes we learned that a layer of frost the thickness of sandpaper on your wings will increase drag 40%, a fairly significant amount. Of course that would be a heck of a lot of dirt to get a layer that thick. Not to mention that drag increases exponentially with velocity, and the planes we fly cruise at around 120mph.

So I would venture to say that it would help, but not even enough to pay for the washing and waxing. My car is pretty dirty right now, maybe I'll test it out.

Shawn D. 07-01-2008 04:42 PM

Quote:

Originally Posted by jesse.rizzo (Post 40091)
In my aviation classes we learned that a layer of frost the thickness of sandpaper on your wings will increase drag 40%, a fairly significant amount. Of course that would be a heck of a lot of dirt to get a layer that thick. Not to mention that drag increases exponentially with velocity, and the planes we fly cruise at around 120mph.

So I would venture to say that it would help, but not even enough to pay for the washing and waxing. My car is pretty dirty right now, maybe I'll test it out.

Yes, BUT as I said -- friction drag on cars is negligible. Friction drag on aircraft is NOT negligible. It's not the same situation.

ebacherville 07-01-2008 04:48 PM

it really is amazing how much resistance picks up over say 60 mph.. riding a motorcycle really educates you on the increases of wind resistance in faster speeds.. cant even imagine these land speed motorcycle guys..

cfg83 07-01-2008 05:31 PM

ebacherville -

Quote:

Originally Posted by ebacherville (Post 40101)
it really is amazing how much resistance picks up over say 60 mph.. riding a motorcycle really educates you on the increases of wind resistance in faster speeds.. cant even imagine these land speed motorcycle guys..

Hmmmmm. *If* I was interested in the best MPG at 70 MPH (65 MPH Max + 5 MPH over), then maybe a wash and wax would just barely begin to help?

CarloSW2

cookie96civic 07-01-2008 06:39 PM

It must be right, I rinsed the sawdust off my car, easily a 9-12 mpg improvement. Oh yeah, looks like the water must have freed the e-brake too, sweet.

Bror Jace 07-01-2008 07:35 PM

"drag increases exponentially with velocity"

That's the key. Spend lots of time at or above 100mph? Then washing and waxing becomes crucial. I'm always amazed when I look at older aircraft with exposed rivets, etc ... what a waste of efficiency! :mad:

Volones 07-02-2008 12:30 AM

I don't think you'll see a noticable difference after washing/waxing.

I just got my best tank ever (44+), and my car is VERY dirty. :)

justpassntime 07-02-2008 12:56 AM

Send me some dirt...
 
Volones,

Can you send me some Colorado dirt for my car? :D


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