Has anybody ever inflated there bicycle tires with water and done a power study

Discussion in 'Cycling Equipment' started by howardjd, Apr 16, 2013.

  1. howardjd

    howardjd New Member

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    High my name is Jason Howard and I am a physics student at University North Carolina Greensboro. I used to compete in triathlons and time trial bike races but have been injured for several years and may be not able to ride competitively again.

    To the point, in 2010 I heard about Sosenkas 3.2 kilo wheel and about Mosers huge fly wheel which got me interested in the effects of wheel inertia on cycling performance. To test this I tested water inflation (which put the wheels at 5pounds) vrs air inflation. When I did a controlled study I time trialed a 9 mile return to start gently rolling course at 300watts once for each set up, the water actually came out about 15sec faster. I have personally constructed a 7 pound(the chunky churner) and 12pound(the air hammer) disk. Before I got injured I managed to race the 7 pound three times and claimed a age group time trial record at the Lowe's motor speedway and posted some good times at triathlon races. The most significant advantage I found from riding the heavier wheels was enhanced gyroscopic stability and being able to ride completely straight with more ease. Due to my injury, its been 2.5 years now an my groin just now doesn't ache all the time, I have been very limited in further testing.

    So the question is whether anyone else out there has experimented with water inflation before on a return to start course(zero net elevation gain). If not would anybody be willing to conduct such a study using power to further investigate the effects of wheel inertia on cycling performance.

    Also I've been told water should have a higher Crr because it is a incompressible fluid but have not been able to find any concrete evidence to back this up. My infield studies certainly did not find and such loss.

    I'm currently writing a paper on this subject and would like as much IN FIELD information about this topic. I'm well aware this is a touchy subject and people have alot of opinions on it so I would like the info to come from personal experience in the field testing wheel inertias.
     
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  2. novetan

    novetan New Member

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    It's "their" not "there"
     
  3. howardjd

    howardjd New Member

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    yeah I caught that, lousy grammar on my part
     
  4. maydog

    maydog Well-Known Member

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    A physics student should be able to understand the large margin of error on your previous "experiments". Averages power measurements do not take in account enviromental changes (wind, air density etc.) or how you applied that power over the course.

    Heck, maybe adding weight may help on a completely flat course - but you need to develop a model to prove that out to everyone else. The accepted and well proven notion is that lighter is faster; there are good models and experimental results that support this.

    I would suspect that water in the wheels would result in more rolling losses due to turbulent flow - but my fluid dynamics experience is very limited.
     
  5. howardjd

    howardjd New Member

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    All true but testing this in field is very difficult to control all the variables and obtain equipment that doesn't change any of them. I'm well aware of the margin of error thing. Can you suggest a better way to test wheel inertia over a broad range of values, meaning by changing wheel mass by increments of kilos and not grams. I really don't know of any where you don't change either the rolling resistance by means of tire or aero dynamics from wheel type.
     
  6. 531Aussie

    531Aussie Well-Known Member

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    Even though you didn't want hill stuff, these guys did a test on Alpe d'Huez (at least it's somethin').
    While apparently trying their best to keep the power output the same, they timed a rider climbing on, 1) a bike with 1.8 litres of water in the tyres; 2) the same setup, but with the water in bottles instead of the tyres; and, 3) the same bike, but with no added water.


    http://www.training4cyclists.com/how-much-time-does-extra-weight-cost-on-alpe-dhuez/
    There are several comments at the bottom of the article
     
  7. alienator

    alienator Well-Known Member

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    Yeah, that was a test that probably seemed like a good idea to someone, but it was one that was pretty poorly thought out.
     
  8. alienator

    alienator Well-Known Member

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    Another double post.
     
  9. howardjd

    howardjd New Member

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    I was thinking if I do the test in the future it will just test whether which is faster water or air. Not necessarily about higher or lower inertia, just to test the variable of whether the substance of inflation has an effect on performance. Someone also suggested as a joke to test chocolate pudding or beer. I also want to test vegetable oil.

    So what do you hypothesize as the best fluid of inflation Air, pudding, beer, or vegetable oil? LOL. Darn it injury I have serious science to attend to!
     
  10. howardjd

    howardjd New Member

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    Yeah I've seen this. What would be interesting is to see this test where they turned around and came back down to finish where they started. Thinking along the lines of the work energy theorem I'm more interested in zero net gain in elevation courses, It can be hilly just no gain or loss therefore no work was done by or against gravity.
     
  11. alienator

    alienator Well-Known Member

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    Unfortunately, thermodynamic realities--the second law of thermodynamics-- demand that more energy be expended when climbing than can be converted to forward motion on the descent. Both the ascent requires excess work (energy) be done to overcome rolling resistance, aero drag, bearing drag, seal drag, and other losses. On the descent some potential energy gained via ascent is lost to overcome the same things: rolling resistance, aero drag, bearing drag, seal drag, and other losses.
     
  12. alienator

    alienator Well-Known Member

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    The best fluid for inflation will be the fluid that has the least friction with the inner tube and the least internal friction. That means that a gas is the best fluid, and as such, liquids are out. As for which gas, it really doesn't matter. Helium wouldn't be a good choice as helium is a difficult gas to contain. That pretty much leaves price as the decider, and in that case air wins since it's freely available via a pump.
     
  13. alienator

    alienator Well-Known Member

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    Another fucking double post.
     
  14. howardjd

    howardjd New Member

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    All true, but all the gravitational potential you loaded yourself up with will be returned to you on the descent to help you overcome these various drags.
     
  15. howardjd

    howardjd New Member

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    Yeah but beer inflation would be a great excuse to have a party.
     
  16. alienator

    alienator Well-Known Member

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    That would be a great waste of good beer.
     
  17. alienator

    alienator Well-Known Member

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    It doesn't matter: you lose energy going up, and you lose energy going down. The net result is that you put in more energy than you get out, and the Second Law of Thermodynamics remains valid.
     
  18. joroshiba

    joroshiba New Member

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    I've always wandered why no one does nitrogen inflated tires, it seems to be the big "thing" to do with car tires. Price obviously would be a factor here, but for some people money seems to be no object.
     
  19. howardjd

    howardjd New Member

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    Yeah I realize all of that. The point is that because gravity is a conservative field if you finish where you start you've done no work in the Gravitational field, you've only expended energy to overcome frictional resistance. Speaking along the lines of the Work-Energy theorem Work is only done in conservative fields(path independent in calculus terms). The frictional losses in cycling in work-energy physics jargin are not technically considered work, they are considered simply frictional losses.
     
  20. alienator

    alienator Well-Known Member

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    It's a big deal in car racing because nitrogen gas is typically dry compared to other gases. Without water vapor, it remains at a pretty stable temperature, and since pressure varies directly with temperature, tire pressure then remains pretty constant. In bicycle tires, that's not an issue, so using nitrogen in bike tires is either a great way to get rid of money or to do something that will yield no real benefits.
     
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