Mythbusters "tests" efficiency of dimples vs. smooth, and clean vs. muddy car

[tasdrouille]

Anyone who knows a thing or two about aerodynamics will tell you dimples do not scale up to work on a car. An 11% increase in FE at 65 mph is more or less between 15 to 20% reduction in drag, that's way too much for not having been universally accepted in the past.

[MadisonMPG]

It's really embarrassing for them to go to an aerodynamic specialist and then fail this hard.

[wagonman76]

They said they couldn't just beat up the car because the metal would stretch and not make a true dimple. The only way I see to duplicate it without clay would be to either mold something... or take off each body panel and make a "dimple die set" and use a press to form the dimples. Or use some thin metal, dimple it with the die set, and then attach it to the car.

The air/water flow test did show improvement with the dimples, but it didn't really look like that much. I too am skeptical about 11%. I wonder what kind of air temperature or wind differences there were between all tests.

[igo]

I think they did a pretty good job with the test. They even kept the clay inside the car for the final test.

I also was amazed that they made it though a whole episode without blowing anything up.

[alohaspirit]

Originally Posted by igo

I think they did a pretty good job with the test. They even kept the clay inside the car for the final test.

I also was amazed that they made it though a whole episode without blowing anything up.

I was a little disappointed with the results. A father test run would have revealed more. But hey gas is expensive. And they have to save money for all the ballistics gel they use.

And I think Grant "blowing up" kinda counts

[shovel]

FWIW I worked with Mythbusters for their "will subwoofers cause an SKS to slamfire" episode (the talkative guy from MTX, Paul, used to be my boss - now I have his job and he's doing product development) - I can say from direct experience that they do not fudge results, make things up, or do any tricks to skew the outcome in any particular direction. The results you see on TV are the results of the testing which they do carry out in earnest.

[pgfpro]

They did a very poor test on this one and should of known better.

The amount of fuel that would be measured roughly would have been .06 lbs total and a difference of .0066lbs or 3 grams of fuel.

They needed to travel a longer distance.

[shovel]

Everyone's a critic

[tasdrouille]

If there was a small effect on the small scale car, it follows that there would be a big effect on a bigger car.

The simplest assumptions often seem the most clever ones. They are also usually wrong.

You're thinking: "How can 800 pounds of clay added to the outside of the car not change its fuel economy?" But you're thinking about it wrong. See, we're not measuring the overall real world fuel efficiency of this car. We're measuring it at very precise conditions, i.e. at 65 mph for exactly one mile. Now I grant you, but the clay on the car, it probably burnt more fuel to get up to that speed, but that doesn't concern us. We expected to see no change with the clay on, and the data bore that out.

Tire pressure didn't change, hence more rolling resistance. The car is definitely sitting lower with 800 pounds on it, hence less aero drag. But then again it's got a slightly larger frontal area. It's kind of surprising all of that evens out, but anyway.

I can see it now, all the NASCARs are gonna be looking like this. What do you think?

I think there's a reason land speed record cars do not look like this.

They like A-B only testing do they. Even the beer-liquor test was done that way.

This is also something interesting...

[nateluke]

Originally Posted by tasdrouille

Anyone who knows a thing or two about aerodynamics will tell you dimples do not scale up to work on a car. An 11% increase in FE at 65 mph is more or less between 15 to 20% reduction in drag, that's way too much for not having been universally accepted in the past.

Possibly, but judging by comments on the internet and even here, it sounds like most people wouldn't want a car that looked like that. Just like the people who think a grille block, mirror delete, etc, looks ugly, despite the real-world gains.

However I do agree with the others that there is a better solution than 850 pounds of clay. I'd drive a dimpled car any day. Kudos to the Mythbusters for testing something useful in a controlled way. Maybe we should get on their message board and suggest they do a full-tank test, or something to that effect for more/better results?