Episode 127: Dirty vs. Clean Car

Air Date: October 21, 2009

A dirty car is more fuel efficient than a clean car because the dirt makes the car more aerodynamic like the dimples on a golf ball.

busted (concept plausible)

Adam and Jamie covered a car in dirt and mud and drove it down a track at highway speeds to measure its fuel efficiency, and repeated the test after the car was cleaned. They discovered that the average gas mileage for the dirty car was 24 miles per gallon while the clean car performed better at 26 miles per gallon. They then tested the reasoning behind the myth, and tested how well dimpled golf balls performed against smooth balls. They discovered that dimpled golf balls could fly almost twice as far as smooth balls. Dimpled balls disrupt the air around them, creating a smaller wake behind them and reducing drag. For a full-scale test, Adam and Jamie put a layer of clay on a car and did two more sets of runs on their track – one with a smooth clay surface, the other with dimples pressed into it. The respective fuel efficiencies were calculated as 26 and 29 miles per gallon. Although the original myth was invalid, the theory behind it was sound, leading to a final judgment of “Busted, Concept Plausible”.

A hangover caused by beer is less severe than one caused by a mixture of beer and liquor.

busted

To perform this test, Tory and Grant would have to eat the same food, drink their alcohol at the same time, and sleep for the same length of time in the warehouse for consistent results. Kari (who could not take part because of her pregnancy) then devised a battery of tests to measure dehydration, memory, light/sound/motion sensitivity, and coordination. Without having drunk alcohol, Tory and Grant performed well on their control test. They then performed the beer test, with Tory drinking 14 cans of beer and Grant drinking six. They both performed significantly worse than the control tests, signifying they were badly hung over. They then repeated the test with a mixture of beer and liquor, making sure to drink an equivalent amount of alcohol as in the first test. The next morning, Tory and Grant improved significantly and felt much better than in the previous test. Thus, the Build Team declared the myth busted.

44 Comments

  1. Nick says:

    I have always heard the statement to be “beer before liquer, never sicker” and “liquer before beer your in the clear” So my question is Did they each drink their shots at the same time or did they mix it up. If you did the shots first the alchohol would hit you faster therefore getting out of your system faster. I would hate to have them test this theory again but I do believe this question significant. Sorry fellas and enjoy once again Kari!!!! Love the show!!!

  2. steven j w says:

    I have been wanting to do the golf ball dimple experiment or see it done for a few years now and finely low and behold you did it. You did a great job. The results were even better than I knew would happen. Now for the fact that a vehicle is not a spinning sphere someone needs to experiment with strategically placing & sizing dimples to get even better results. I know this system would work on a semi truck with great results.
    Fantastic show I wish I could work there with you.

  3. Mark says:

    When I drink on a friday and again on a saturday i can usually drink more on the second night. My question is this, Was there a suficient amount of time allowed between the two drinking tests to assure that the drinkers alcohol tolerance from the first test didn’t affect the second test?

  4. Nelson says:

    That was cool and the results of the dimple car are better than i could of hoped for. I’m going to try it on my next pine wood derby car.

  5. Lidya says:

    was there enough time to get the previous alcohol out of there system? If they did the test the very next day the night before was not over. they have a better tolerance cuz they where just basically drunk for 2 days. It needs to be re=done and which one would be better liquor then beer or beer then liquor? Loved the tests but we need more!

  6. nate w says:

    First off.. love the show, watch it all the time keep up the great work. Now my only question is when doing the golf car… you made it aerodynamic all the way around so it would work. Most dirt and grime is always more on the hood and sides.wouldnt that make it disrupt the flow of air around the car, being that dirt wont be even all the way around the car?

  7. Red says:

    I’ve honestly never heard the beer vs. liquor myth as tested, I have always heard: “Liquor before beer, you’re in the clear; beer before liquor, never sicker.”

  8. Jovan Coates says:

    I wonder if the dimpled car can be re-tested with a car that was hail damaged as most of them have dimples after a hailstorm? Thanks for that I now have some ammunition to use when people make fun of me for cleaning my car so often.

  9. Rich says:

    Unfornately I was tired and fell asleep so I missed the results on it all but I do have a question. Did they have a hang over or were they still drunk? Just curious. What about the supposed affects different alcoholic drinks have on different people… such as the guy who can’t drink whiskey or tequila or XXX etc.. because it makes me mean. Are there different alcoholic drinks that mean worse hangovers? Ok… this could go forever. Great show and congratulations Kari.
    Rich

    P.S. I’d be a bad candiate for the alcohol topic because I get the same results regardless of what I drink and none are near as bad as what they experienced. Not even the one beer I was chasing with tequila in Domician Republic. (El Presidente)

  10. victor says:

    I work for Boeing and was excited to see the dimpled car results. I talked to our aerodynamics group and they were skeptical? The myth is the golf ball needs to be spinning and moving air behind the ball? Please do this on a aircraft to prove these skeptics wrong and help get us greener.

    • Jordan says:

      Definitely a sound idea, except that airplanes fly at high altitudes, where the air gets much thinner, and so there’s less air resistance to reduce in the first place. Therefore, it’s possible that the slight increase in aerodynamic efficiency isn’t worth the effort and energy required to dimple the body of an aircraft.

      But indeed, that just makes a test all the more necessary to see how valid your proposition really is.

  11. Jim says:

    My interpretation of this beer-liquor mantra has always been that it’s about the likelihood that a person who drinks beer and then begins to drink shots will make impaired decisions about how much alcohol they are consuming, drink too much, and get sick. I mean, go to a bar, drink beer, and then decide “woo-hoo! lets start doing shots!!”… you might get carried away there.

  12. ALAN says:

    IT WOULD NOT BE POSSIBLE FOR THE GENERAL PUBLIC TO DO WHAT YOU DID TO THERE OWN CAR. BUT THEY COULD DO JUST THE OPPOSITE. INSTEAD OF DIMPLES THAT GO IN DIMPLES THAT GO OUT.
    I DONT THINK THAT THE MYTHE WAS TOTALLY TESTED WITH OUT KNOWING THAT DIMPLES THAT GO OUT WORK AS WELL AS ONE THAT GO IN.

    MORE TESTING IS NEEDED.

  13. LITA says:

    STICK ON DIMPLES THAT GO OUT COULD BE PUT ON ANY CAR OR TRUCK OR 18 WHEEL TRUCK. IF IT WORKED AS WELL AS DIMPLES THAT GO IN WHAT A WONDERFULL DEAL THAT WOULD BE.

  14. Chris says:

    Per my Fluid Mechanics class a turbulent fluid zone surrounding a moving body produces less drag on the body than a smooth laminar flow. Hence using the dimpled body a turbulent zone is generated and the drag is reduced. I think a semi-trailer or airline fuselage already has enough protruding features like rivits and structural ribs to generate the required turbulence (disrupted laminar flow). The folks who make Airstream trailers might take note of this though and incorporate some drag reducing features on their camper trailers.

  15. Eric says:

    In response to Victor’s comment that the engineers told him the ball would be spinning and moving the air behind the ball. This doesn’t track because they show a ball in a wind tunnel nailed and not spinning and the wake is smaller with an undimpled ball.
    From my understanding, the air isn’t being moved, the low pressure area behind the ball is smaller because the turbulent air follows further around the ball creating a smaller low pressure zone (the low pressure zone acts like a vacuum sucking the ball backwards sapping it’s forward momentum)

  16. Eric says:

    sorry, said that wrong. The wake is smaller with a dimpled ball.

    Probably not clear, but the wake is the low pressue zone behind the ball.

  17. Dimple Bill says:

    This is the first time I have ever responded to any program, but I feel that I have to. You can say what you want about the experement and how it was done, but the results were so dramatic that I think that it needs to be tested further. Bonniville speed week would be a good test. Get one of the participants who have been trying for years to set a record and who had a car with an easily replacable body to try it. If a metal body, a ball-peen hammer would do.
    There would have to be a lot of testing to figure out what would work best, more small dimples or fewer large ones. How deep should they be?
    My theory is that no how slick the surface (with wax or what ever) there still is resistance. With a dimple, however, the air would be moving over the little pockets of gas as opposed to a solid, thereby having less friction.
    Of all the things you have tested, this one may well have the potential of having the greatest impact on science and the reusulting effects on speed and effeciency than anything you have or ever will have done.
    You need to go further on it. Something as simple as a positivie result on a golf ball may lead to one of the greatest discoveries regarding the moving of solid objects through the atmosphere ever tested. Wow, just think of the possibilities!

  18. Chappy says:

    I dont see any problems with the methodology in how they tackled the myths. People might be skeptical of the alcohol myth but I think Jim’s explanation reasonably describes how that saying came to be. I’m sure they posted the detailed methodology on their site…but their site is so hard to navigate.

    The dimples simply re-energize the airflow so it doesnt separate from the surface. The turbulence of the dimples keeps the flow laminar so it sticks to the surface longer and therefore it is less turbulent(the ‘wake’) at the back.

    @Victor – Putting clay on an aircraft would make the aircraft unairworthy and thus it would be illegal to takeoff in. They would require a test pilot and a special flight permit, which might be quite difficult/imposisble for mythbusters. However, since you work at Boeing, you can propose your idea to the company. Or you can just ask Cessna about their hail experience.

  19. jordan says:

    no a clean car has better mileige becase it is not as heavy, as dirty car is a lot heavier so clean car has better mileige than a clean car

  20. Chappy says:

    @Jordan – You mean a dirty car as in the first test or dimpled as in the second. The decrease in mileage in the first test was due to the drag and weight by the mud. The dimpled car in the second test clearly showed an increase in mileage. Did you watched the episode?

    Also, Jamie clearly stated that the test did not include the gas required for acceleration (where weight/mass would be an important factor).

  21. daveroy says:

    Regarding smooth vs dimpled ball,I know the difference would be tiny, but surely if the dimples are produced by drilling, as with the bowling ball and car models, weight would have to come into the equation.

  22. Royeddie says:

    My only criticism is with the timing method. Judging when to switch on and off could be quite inaccurate, even though the inaccuracy would be ironed out over the five runs, it could still make a significant difference. It would be more accurate to use an infrared beam to switch the fuel flow on and off.

  23. Paul Malley says:

    Mixing Beer and Whisky is known as a whisky chaser.

    The English and various other effete Continental
    types( I wouldn’t know about the Yanks) will dilute their scotch with a fizzy sweet carbonated
    cordial in order to make a “long” drink out of it.

    A Scot on the other hand will drink his beer and
    taste it then drink his whisky and taste it, then
    drink his beer and taste it and so on.
    Are you starting to get the Idea?

    If you wish to mix your alcohols mix grain alcohol
    with grape alcohol.

    Now there’s a headache

  24. nick says:

    Sadly, i think the alcohol myth was miss-interpreted in this challange… The statement i always heard was “Liquor before beer your in the clear, beer before liquor never been sicker”. That is, its a warning as to how to drink the alcohol and not being sick from drinking too much.

    Mainly being that you have a lot of carbs from drinking beer and there is more substance to it, so you will not be able to consume as much as you would of the hard liquor counterpart in that same amount of time. The thought is that beer takes longer to get into your blood stream, much like if you eat something while drinking a hard liquor.

    And if that is true, you have one even curve towards being drunk with beer, as you need more time after consuming the beer to “feel” it affecting you than you do in say whiskey.

    So if you are consuming whiskey you can feel how drunk each drink is making you, and then if you stop drinking that, and start drinking beer, you are not only adding something with substance to your stomach, but also alot of water. So you will still be on an even curve of knowing your tolerance before you become sick.

    On the other hand, if you drink beer, where you might consume more alcohol than you can yet feel as your stomach is still digesting and absorbing it, then you follow that with hard liqour, till you “feel” you have reached your limit and your body then continues to process the remaining beer and at that point you have started urinating alot of the water out… making it far easier to get more drunk than you plan to get, and very very sick because of it….

    You would need to test to find the approximate ingested alcohol percentage of tolerance of each person, then divide that up between beer and whiskey, and drink them one way first, beer then whiskey, then the other way, whiskey then beer, and see how they drunk they feel as the night continues…

    Just my 2 Cents…

    Keep up the myth-busting…

  25. Glenn A says:

    I think you did it backwards. Hate to put the boys through it again but I think you need 5 tests:
    A control
    Beer only
    Whisky only
    Beer before whisky and
    Whisky before beer.

    The saying I have always lived by and confirmed personally by multiple experiment is “BEER on Whisky, Mighty Risky. Whisky on beer, never fear.”

    Carbonation speeds the absorption of alcohol, so drinking beer then liquor would cause the more concentrated alcohol to be absorbed at a faster rate than it would normally.

    Also people tend to drink liquor faster than beer so switching to liquor from beer is likely to speed the rate of liquor consumption. Also alcohol is metabolized faster when the body is active. If the more concentrated alcohol is consumed later in the evening you have less time to burn it off before going to bed.

    OTOH, starting with hard liquor slows the rate of consumption. The alcohol in beer is less concentrated so the actual rate alcohol is consumed reduces as the evening progresses and the body has more time to metabolize it while you are still burning calories. Also By increasing the water intake from the beer after consuming the more concentrated liquor you assist in re hydrating the body.

  26. jim says:

    there is a company that makes a dimple wall paper that goes on trucks and trailers and hi speed trains and improves fuel milage cars could be next

  27. Glenn Beard says:

    The type of alcohol you drink does affect the severity of your hangover. Soomething like vodka, which mostly pure alcohol, produces less severe hangovers than bourbon. The results of a recent study of vodka versus bourbon stated “No effect of beverage congeners was found except on hangover severity, with people feeling worse after bourbon” I read the same thing more than 20 years ago, where my pyschology professor ran a similar test. The study I cited was from 2009, and can be found below.

    “Intoxication With Bourbon Versus Vodka: Effects on Hangover, Sleep, and Next-Day Neurocognitive Performance in Young Adults” Damaris J. Rohsenow, Jonathan Howland, J. Todd Arnedt

  28. Bill M., Penfield, NY says:

    Could you perform a myth busters episode where you compare, for the same force, which ball drives further: either (A) a standard golf ball with dimples going in, or (B) a golf ball with dimples that go out? I did a quick google search and couldn’t find a case where someone has already done this test. I would suggest that you use a machine to drive the balls so that you can be sure that the exact same force was being used for each swing of the golf club. My guess is that both balls would drive the same distance (assuming that the dimples that go in are the same size as the dimples that go out)…but I’m not sure. If a ball with “dimples going out” drives further than “dimples going in,” maybe your show could change the game of golf…and how cool would that be!

  29. Geoff says:

    I think you should apply the dimpled car test to a NASCAR race car and see if the fuel economy improves and if the top speed increases over 10 high speed laps at a long track, like a 2 mile or longer. Body parts on a race car are easily replaceable, so making custom dimpled panels to fit the car should not be to difficult.

  30. Logak says:

    Could someone make an entire dimpled car body? That is, not having to add clay or panels, but have it actually come out of the shop with the metal on the body already incorporating dimples? It seems to me that theoretically it should be possible to do this. That alone could get car manufacturers partway towards their mileage standards.

  31. michael says:

    on the achol myth
    they said they they left “enought time to recover” I asume that means at least a couple of days and I seam to have gotten the thought (I will have to rewatch) that it was a week but I think there sample size was to small it might just have been chance that there hangovers where worse and they defently need to to the “don’t mix grape and grain” myth

  32. Victor says:

    About the dirty car myth, Adam and Jamie did a great job! But why there’s no racing car like F1 apply this? Dimpled panel aren’t hard to make.

  33. Someone says:

    To Victor:
    They didn’t say dimpled panel will increase the “speed”, just the fuel efficiency. For racing cars, fuel efficiency is not important at all. Speed is everything.

    • Bronco says:

      To someone;
      Increasing fuel efficiency means you are using less power from the engine to maintain the same speed, so therefore it should also mean more speed, perhaps that’s Red Bull’s secret???

  34. Nick L says:

    I don’t know if people from the show will read this but I agree with people above on the alcohol myth.

    I have never heard stick with beer your in the clear…the saying goes beer before liquor you’ve never been sicker and liquor before beer your in the clear. This has nothing to do with only beer, it has more to do with the order that you drink the different types of alcohol. This needs to be redone because I would like to see what type of results they get. I lean towards this saying being true based on personal experience!

  35. Caitlin Jacks says:

    So the saying goes “Beer before liquor never been sicker, liquor before beer your in the clear.” My question is, is this myth or fact because personaly I think it’s fact and I would really like to know if it is.
    P.S. I love the show =)

  36. Darren says:

    The hangover test is flawed in that it doesn’t recognize people build up a tolerance or immunity following a night of drinking. For example, if I know I’m going to have a lot of drinks at New Year’s Eve, the night before will have a few drinks just to get my body prepared for the shock. It makes a huge difference to the damage done.

    I think I picked up that trick from a medical or science article I read once. I can verify it from many tests. I thought people knew that.

    Love the show.

  37. Jordan says:

    I think the dimpled car test worked so well that they should try sending the idea in to actual car companies, challenging them to make car bodies with dimpled surfaces.

  38. Steve M says:

    First I was surprised clay has lower drag coefficient of resistance than steel, I assumed the clay car weighed more, and had a higher surface area.
    Second the true comparison has to be building the dimples out. This is harder to do, but if you have dimples, you can have a smaller, lighter car.
    With a golf ball the dimples work because they allow for a larger impact area, and reduced drag.

  39. J says:

    Hangover test was also flawed because the quality of the beer vs liquor was not comparable. From what I could tell, they were drinking something terrible like miller or bud, but drinking much higher shelf liquor. A well made microbrewed lager or pils would have significantly less sugars and impurities, thus less of a hangover. Try the test with plastic bottle whiskey and see how bad the hangover is…

  40. jozh says:

    In the 80ties Schubert sold a golf ball motorcycle helmet:

    http://xjfahrer.bboard.de/board/ftopic-62987920nx52848-7707.html

    I had one and it was really a difference wearing it at a speed over 120 km/h (75mph).

  41. Max says:

    Can someone explain how the result of the beer & liquor myth works?

  42. Oliveira says:

    Car with golf ball skin. The skin shape depends on the size of the car and the velocity of the car. Hint: watch the pattern on dunes or desert sands or just put sand on a wind tunnel…

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