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Old 05-01-2010, 01:03 AM   #1 (permalink)
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Another mythbusters video: +11% fuel economy

This is crazy, but the mythbusters covered a car in clay, put dimples in it like a golf ball, and gained fuel economy, despite adding a bunch of weight!

What if they had used spray foam and used something to harden it? I know they're not experts, but to show real results like that is something interesting.

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I think you missed the point I was trying to make, which is that it's not rational to do either speed or fuel economy mods for economic reasons. You do it as a form of recreation, for the fun and for the challenge.
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Old 05-01-2010, 01:49 AM   #2 (permalink)
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Been covered in quite a few threads here... We don't take MB seriously, because their testing procedures are anything short of scientific. The show is there for the fans, not to actually solve anything. If they happen to stumble onto something in the mean time, it's just goodie points for them.

I hate to seem so brash about it, but it's honesty.
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Old 05-01-2010, 02:10 AM   #3 (permalink)
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^I concur...way too many variables could have caused the slight mpg increase, such as how the driver drove during that trip compared to the other two drives, if there was any winds to come up, and just the fact they did such a small amount of driving. A few trips with more miles and gallons being used would give a better account than just a few grams worth of fuel.

And even if it did work, well, we may do wacky things to our cars to get lots of MPG but even we have some dignity!
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Old 05-01-2010, 11:04 AM   #4 (permalink)
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That's funny, I would have never thought that 11% would be considered a slight uptick in economy. From what i understand they did 3 sets of runs, one with the car stock, one with the car covered in clay and undimpled, and the last with the dimples. From what I understand, each set consisted of 5 "laps" I guess you could say.

I agree that a lot of what they do doesn't cover all the variables. But golf balls do have dimples for a reason, so why couldn't the theory be applied to something larger?
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I think you missed the point I was trying to make, which is that it's not rational to do either speed or fuel economy mods for economic reasons. You do it as a form of recreation, for the fun and for the challenge.
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Old 05-01-2010, 01:19 PM   #5 (permalink)
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Does your car regularly go 120 mph and spin end over end whilst doing so?
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Old 05-01-2010, 01:33 PM   #6 (permalink)
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Quote:
Originally Posted by ShadeTreeMech View Post
This is crazy, but the mythbusters covered a car in clay, put dimples in it like a golf ball, and gained fuel economy, despite adding a bunch of weight!
The weights were the same because they measured the mileage after the clay was put on (smooth), then put the clay they cut out of the dimples into the back seat.

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Does your car regularly go 120 mph and spin end over end whilst doing so?
Irrelevant as long as the Reynolds numbers are similar.
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Old 05-01-2010, 02:08 PM   #7 (permalink)
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Possible variables that were not accounted for:

1) Warmer pavement, warmer tyres, lower RR, better FE
2) Warmer car. bearings, engine, transmission, all warmer later in the day, Better FE
3) Driving technique
4) Wind
5) Air density

Just a few.
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Old 05-01-2010, 04:31 PM   #8 (permalink)
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Quote:
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Quote:
Originally Posted by MadisonMPG View Post
Does your car regularly go 120 mph and spin end over end whilst doing so?
Irrelevant as long as the Reynolds numbers are similar.
As long as the Reynolds number and the shape are similar, which they are not.

You could expect cars with a round rear end, like a Taurus, to behave somewhat like a golf ball and benefit from carefully placed vortex generators near the trailing edge. You should not expect VG's to benefit cars that already have good aerodynamics, though.

Due to their lack of scientific rigor, Mythbusters stopped short of conclusively proving anything, though.
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Old 05-02-2010, 05:43 PM   #9 (permalink)
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Quote:
Originally Posted by MadisonMPG View Post
Does your car regularly go 120 mph and spin end over end whilst doing so?
LOL that made my day! thanks for a good laugh!

But I do wonder what the airflow over a vehicle with oversized divots would be like.

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I think you missed the point I was trying to make, which is that it's not rational to do either speed or fuel economy mods for economic reasons. You do it as a form of recreation, for the fun and for the challenge.
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