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Thread: Dirt is good?!

  
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    d_ghedia's Avatar
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    Dirt is good?!

    Saw this on Auto Express.... made me chuckle! Haven't Scientists got any thing better to do?

    Don't bother polishing your car - it wastes fuel! Scientists have discovered that rough surfaces can be more aerodynamic than shiny ones by helping vehicles slip through the air more efficiently

    If the bumps are the size and shape of tiny cylinders, they keep the air flowing around the car. "This goes against conventional thinking," said Swedish researcher Jens Fransson.


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    hmmmmmmm so the added weight of all the muck (probably would be quite a suprising amount if your car was filthy) would then counteract the 'fuel saving' of not washing your car.

    like you say, scientists have nothing better to and get paid way to much to find out this sort of dribble! probably some fat, lazy bloke trying to 'prove' why he shouldn't wash his car to his nagging wife

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    This is actually very true - look at a golf ball. Those dimples help if fly further by reducing drag. Would be a pain polishing a car with golf ball style dimples though.
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    lol the same people who think autoglym super resin polish is the same as turtle wax, wax.

    They should stick to something they know about, I do design engineering at uni and we have started CFD, which is the study of fluid/gas across a body and there is no way a rough surface helps aerodynamically and how you are supposed to achieve cylindrical pieces of dirt is beyond me.

    Autoexpress should stick to what they know, which seems to be not a lot.
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    But by keeping a turbulent layer over the surface, surface tension is reduced. (on a golf ball at least). A bit like headwork - you should not polish the inlet side as it increases surface tension and slow the air. The inlet should always have a satin rough finish.

    PS. I'm a hydraulics engineer. ;p
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    Isn't this a similar concept to a shark having skin like sandpaper? I know water and air are 2 different mediums, but I believe similar principles apply. There's talk of making the outside of warship hulls have the same properties and Speedo made a swimsuit that was quicker than a normal one.

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    Quote Originally Posted by MikeWarner
    But by keeping a turbulent layer over the surface, surface tension is reduced. (on a golf ball at least). A bit like headwork - you should not polish the inlet side as it increases surface tension and slow the air. The inlet should always have a satin rough finish.

    PS. I'm a hydraulics engineer. ;p
    I doubt that autoexpress have got the facts right in the first place but I even doubt it will give you more MPG.

    Personally I prefer a clean car, I guess its another thing to think about. lol.
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    SXi Stu
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    alot of boats have rough hulls to help cut throught the water better, the dirt idea still sounds a bit ridiculous to me mind!

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    Quote Originally Posted by SXi Stu
    alot of boats have rough hulls to help cut throught the water better, the dirt idea still sounds a bit ridiculous to me mind!
    I think thats the thing, they apply it in a controlled enviroment, whereas autopexpress try and say that driving down the road will have the same effect.
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    Quote Originally Posted by JJ_
    I think thats the thing, they apply it in a controlled enviroment, whereas autopexpress try and say that driving down the road will have the same effect.
    Agreed, a randomly dirty car is not going to reduce drag.
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