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An Aerodynamic Device or Fender

  1. Sep 11, 2011 #1
    Please advise if the plastic white component mounted below the number plate on these motorcycles is or is not an Aerodynamic device that could afford an advantage at 100+ MPH over an identical motorcycle without this device? Users claim it is to keep dirt out of the hole in the bottom of the neck of the triple trees that hold the forks. I submit, if that be the case, why not just simply use a piece of lightweight tape instead of this heavier part?

    The components in question are below the number plates on the #4 and #59 Motorcycles. I submit they re-direct air downward, thus avoiding the fins of the cylinder on the engine, and force it to run under the chassis, where it creates far less drag than running through the fins on the cylinder.

    http://amaproracing.com/images/content/story/Springfield_featured.jpg [Broken]

    American Motorcyclists Association AMA in Daytona Florida Tech Directors state that they feel this device affords zero aerodynamic advantage. And they also contend that it is not a fender to keep dirt off the lower Triple Trees. We are trying to determine just what the hell this thing is then?

    Thanks in advance for your input.
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Sep 11, 2011 #2
  4. Sep 11, 2011 #3


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    My opinion is that this feature will not give any discernible aerodynamic advantage on those bikes (with wide bars, tyres, no fairings, race numbers etc), but you'd need at least a CFD study (and possibly a wind tunnel test) to tell for sure.
  5. Sep 11, 2011 #4
    I looks more like it would redirect airflow over the engine to cool it down better.
  6. Sep 11, 2011 #5
    The finish in these races after 25 laps on a mile dirt oval is .001 - .045 seconds at the finish line for the top five bikes. Last race the finish difference was .000 measured using AMB-IT Transponders. Photograph was used to determine the winner.

    With that said, if this component would reduce drag at any percentage, it could make the difference in the outcome of one of these contests.

    Looking at this CFD Study, one notes that a very minor change in shape of the SUV body, reduces drag.

    http://csus-dspace.calstate.edu/xmlui/bitstream/handle/10211.9/123/Thesis - Final.pdf?sequence=1
  7. Sep 11, 2011 #6


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    You can't take a study done on an SUV and apply it to a dirt bike. They are totally different animals. Honestly, like brewnog said, based on the information you have provided I can't think of any possible aerodynamic advantage to the part in question.
  8. Sep 11, 2011 #7
    More no the machines these are mounted on.
    While they race on hard packed clay surfaces, these machines exceed 145mph on the long straights. They are not Dirt Bikes like Moto Cross. Over 100hp weighing 300lbs, they race on oval tracks, many used for horse racing. Drafting to the finish with six or more in line is common for the 25 laps on the Mile tracks. Typical finish has four or five crossing the finish line less than .003 seconds apart at over 140mph.
  9. Sep 12, 2011 #8


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    And despite all of that, there is still no discernible aerodynamic advantage conferred by these devices. I am sorry, but unless you hire someone to do a full CFD analysis, the best we can all say is that it appears to not offer an advantage.
  10. Sep 12, 2011 #9
    It looks to me like protection for the fork suspension. You don't want rocks and other debris denting or damaging your shock/suspension rods.

    Its a rounded cover for a thinner, rounded rod, I doubt it has any positive aerodynamic effects.
  11. Sep 12, 2011 #10
    Just curious, but what is your personal concern? Are you a rival competitor?
  12. Sep 13, 2011 #11
    That and keep spray from the tires in wet weather out of the rider's face.
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