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Old 10-18-2009, 10:42 AM   1 links from elsewhere to this Post. Click to view. #1 (permalink)
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Mythbusters "tests" efficiency of dimples vs. smooth, and clean vs. muddy car

Admin note: 2 threads were started on this topic. The other one is here: Mythbusters tests "golf ball" dimples

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I don't watch the show regularly, but this one might be worth tuning in for the entertainment factor.

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Discovery Channel :: TV Listings :: MythBusters

Oct 21, 9:00 pm

Adam and Jamie get down and dirty with the myth that a muddy motorcar gets better gas mileage than it's clean cousin.
Also.. don't they have it backward? Isn't the common myth that the clean car gets better mileage?


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Old 10-18-2009, 11:50 AM   #2 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
Also.. don't they have it backward? Isn't the common myth that the clean car gets better mileage?
Hmm, I can imagine having enough mud buildup in the wheelwells to reduce the distance between them and the wheels. Or mud sticking to the rear of the car, drying and hardening, layer on layer, in the shape of a Kammback extension. But by the time either of these would have a noticeable aero effect, the weight penalty would start to be a pain.
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Old 10-18-2009, 02:53 PM   #3 (permalink)
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I will be watching it. I love mythbusters even tho they seem to be obsesed with explosions.
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Old 10-18-2009, 03:50 PM   #4 (permalink)
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Quote:
Originally Posted by igo View Post
I will be watching it. I love mythbusters even tho they seem to be obsesed with explosions.
I love Mythbusters BECAUSE they seem to be obsesed with explosions... hehehee
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Old 10-18-2009, 04:04 PM   #5 (permalink)
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I think the muddy/clean thing is like the golfball dimple theory. Sometimes rough is better than smooth. I'm actually looking forward to this one...

If it works you could cover your car with rocker guard or ceiling texture and paint over it. Might look kind of cool.
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Old 10-18-2009, 05:04 PM   #6 (permalink)
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They are supposed to be "dimpling" a car, I think.
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Old 10-18-2009, 05:11 PM   #7 (permalink)
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Originally Posted by MadisonMPG View Post
They are supposed to be "dimpling" a car, I think.
...so instead of "Body by Fisher" it'd be "Body by Top-Flite" (ha,ha)!
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Old 10-18-2009, 05:32 PM   #8 (permalink)
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I could just see them firing golf balls at a car to get the dimples.
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Old 10-18-2009, 05:35 PM   #9 (permalink)
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SOunds like a hail storm car to me!

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Old 10-18-2009, 09:46 PM   #10 (permalink)
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I'm sure it'll be entertaining and worth watching.

I predict their conclusion will be "we can not detect a fuel economy difference between these two cars".

It would take a pretty extreme setup to do aerodynamic testing sensitive enough to detect mud. A wind tunnel would do it, but they wouldn't take a car to a wind tunnel for a simple myth like this. Short of that, you'd need high speed bidirectional coastdown testing on a totally windless day. Even if you accounted for airspeed, small crosswinds would skew your results beyond utility.

As to the effects of mud: It tends to increase the car's frontal area, obviously. Cakes of mud on streamlined surfaces will increase your Cd, while cakes of mud in your eddies will tend to decrease your Cd. A muddy truck with its panel gaps and hood cowl filled with mud will probably get better gas mileage, but unless your aeromodded Metro gets a teardrop-shaped tail made of mud, it's likely to get slightly worse gas mileage when muddy.
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