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  1. #1
    モㄥ工匕モ 爪モ爪乃モ尺 evilcryalotmore's Avatar
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    Today in physics i learned that solid disc's spin faster then hollow discs.

    Disc rim VS traditional laced rim?

    I learned that a solid disc will always spin faster due to the center of gravity.

    You think this would apply verywell with a disc rim?

    I've done multiple tests in class, And it's so far been proven true. I would do the test with a disc and traditional lace. But that means i need a mirror surface large enough for the rim, And i would need to spin the rims on its lip not tires ):

  2. #2
    . bbattle's Avatar
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    Spokes have more air resistance than the disc; cyclists learned this long ago. They also learned that in crosswinds, the fool with disc wheels is in trouble. Back in the '80's, they ran time trials in the Red Zinger races with disc wheels on the front. In Colorado. Where the wind never blows. yeah, right. They no longer do such foolish things. But you do see roadies with 40-60mm deep rims.

  3. #3
    King of the Hipsters
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    Quote Originally Posted by evilcryalotmore View Post
    Disc rim VS traditional laced rim?

    I learned that a solid disc will always spin faster due to the center of gravity.

    You think this would apply verywell with a disc rim?

    I've done multiple tests in class, And it's so far been proven true. I would do the test with a disc and traditional lace. But that means i need a mirror surface large enough for the rim, And i would need to spin the rims on its lip not tires ):
    Where do you study physics?

  4. #4
    Veteran Racer TejanoTrackie's Avatar
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    Oh boy, this could get ugly.
    What, Me Worry? - Alfred E. Neuman

    Quote Originally Posted by Dcv View Post
    I'd like to think i have as much money as brains.

  5. #5
    Me!! KyleOndy's Avatar
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    Quote Originally Posted by evilcryalotmore View Post
    Disc rim VS traditional laced rim?

    I learned that a solid disc will always spin faster due to the center of gravity.

    You think this would apply verywell with a disc rim?

    I've done multiple tests in class, And it's so far been proven true. I would do the test with a disc and traditional lace. But that means i need a mirror surface large enough for the rim, And i would need to spin the rims on its lip not tires ):
    For wheels of equal mass and uniform mass distribution this is true. So you can't just slap on a cover and magically reduce the wheel's moment of inertia.
    Quote Originally Posted by dysFTP
    lose your fear of death and the soreness will go away.

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    Constant tinkerer FastJake's Avatar
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    Quote Originally Posted by KyleOndy View Post
    For wheels of equal mass and uniform mass distribution this is true. So you can't just slap on a cover and magically reduce the wheel's moment of inertia.
    Exactly. Plus, you can't really model a spoked wheel as a "hollow disc" because it isn't. The rim alone might be, but it has all the spokes and hub attached to it.

    I think Post #2 sums it up pretty well. Although I'd still like to try a rear disc wheel on my roadie and see how it works. I've been thinking about making my own wheel covers, just out of curiosity.
    Why "derailer" is the correct way to spell the gear-change mechanism: sheldonbrown.com/derailer.html

  7. #7
    GONE~
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    Post the numbers of your tests please.

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    モㄥ工匕モ 爪モ爪乃モ尺 evilcryalotmore's Avatar
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    Huh, Just wondering because i had done this inscale with a uiler's disc one hollow ring and one disc, And the disc almost spinned for over 3-4 minutes.

    How about those fancy rims i see that are semi disc. They have 4 small small holes maybe 2-3 inches for air to go through.

  9. #9
    Me!! KyleOndy's Avatar
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    What axis were you spinning them on?
    Quote Originally Posted by dysFTP
    lose your fear of death and the soreness will go away.

  10. #10
    Constant tinkerer FastJake's Avatar
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    Quote Originally Posted by evilcryalotmore View Post
    inscale

    a uiler's disc

    the disc almost spinned
    I'm so confused! Maybe you should pay more attention in English?
    Why "derailer" is the correct way to spell the gear-change mechanism: sheldonbrown.com/derailer.html

  11. #11
    Veteran Racer TejanoTrackie's Avatar
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    Quote Originally Posted by FastJake View Post
    Although I'd still like to try a rear disc wheel on my roadie and see how it works. I've been thinking about making my own wheel covers, just out of curiosity.
    Rear discs are used routinely on outdoor tracks, where it can be windy, so I don't imagine it would be a problem on the road. However, most of the aerodynamic benefit comes from the front wheel, so IDK if you will notice a very significant improvement. What does make a big difference IME is using bladed / oval spokes instead of round spokes and to minimize the spoke count in the front and to a lesser extent in the rear. Finally, use the narrowest possible front rim and tire.
    What, Me Worry? - Alfred E. Neuman

    Quote Originally Posted by Dcv View Post
    I'd like to think i have as much money as brains.

  12. #12
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    It doesn't matter if you can spin the disc faster, it's different when it is on a bike with wind resistance, road resistance, drivetrain of the bike, physical condition of the cyclist etc etc.

    Bunk test is bunk.

  13. #13
    Me!! KyleOndy's Avatar
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    If you are talking about an Euler Disk, http://www.youtube.com/watch?v=ug2bKCG4gZY, Thats a whole different ball game of physics.
    Quote Originally Posted by dysFTP
    lose your fear of death and the soreness will go away.

  14. #14
    Constant tinkerer FastJake's Avatar
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    Quote Originally Posted by TejanoTrackie View Post
    Rear discs are used routinely on outdoor tracks, where it can be windy, so I don't imagine it would be a problem on the road. However, most of the aerodynamic benefit comes from the front wheel, so IDK if you will notice a very significant improvement. What does make a big difference IME is using bladed / oval spokes instead of round spokes and to minimize the spoke count in the front and to a lesser extent in the rear. Finally, use the narrowest possible front rim and tire.
    Does my Specialized tri-spoke count? According to this: http://www.sheldonbrown.com/rinard/wheel/grignon.htm it's pretty aero.

    Still, it can really throw me around on windy days. I can't imagine using a front disc outdoors.
    Why "derailer" is the correct way to spell the gear-change mechanism: sheldonbrown.com/derailer.html

  15. #15
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    tomorrow i learned in calculus that skinny jeans have a lower drag coefficient than baseball caps leading to higher fuel efficiency

  16. #16
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    Quote Originally Posted by FastJake View Post
    Does my Specialized tri-spoke count?
    Does it wooosh when you bomb a hill?

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    Veteran Racer TejanoTrackie's Avatar
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    Quote Originally Posted by FastJake View Post
    Does my Specialized tri-spoke count? According to this: http://www.sheldonbrown.com/rinard/wheel/grignon.htm it's pretty aero.

    Still, it can really throw me around on windy days. I can't imagine using a front disc outdoors.
    Sure, its very aero, which is why triathletes use them, but in the front any solid spoke wheel, just like any deep section wheel is going to be hard to control in the wind. I used to own a Mavic IO front 5 spoke solid carbon wheel and it was murder to control on windy days. But on calm days there was nothing faster.
    What, Me Worry? - Alfred E. Neuman

    Quote Originally Posted by Dcv View Post
    I'd like to think i have as much money as brains.

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    Quote Originally Posted by xkillemallx16 View Post
    tomorrow i learned in calculus that skinny jeans have a lower drag coefficient than baseball caps...
    duh.

    that's why i wear a fidel hat.
    Last edited by dookie; 01-26-11 at 09:03 PM.
    Quote Originally Posted by politely removed
    I am ****ing devoted too. I am moving into my friend's closet just so I can save up for bike stuff.
    well, here's some for you! everything's for sale...

  19. #19
    Senior Member Shimagnolo's Avatar
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    Quote Originally Posted by bbattle View Post
    Back in the '80's, they ran time trials in the Red Zinger races with disc wheels on the front. In Colorado. Where the wind never blows. yeah, right.


    My regular ride includes the Morgul Bismarck from the old Red Zinger races.
    Not only is it windy as holy hell in the winter, there are always a few days every winter when I must give up and turn around because it it literally impossible to keep from getting blown off the road on the Northbound leg.
    You couldn't pay me enough to run a disc.
    I won't even use Deep-V's.

  20. #20
    Elitist carleton's Avatar
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  21. #21
    i smell bacon yummygooey's Avatar
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    I'm glad that you're trying to apply what you learn in class to real life, but you should do some more reading one why a solid disk will spin longer than a hoop. Your experiment probably had nothing to do with aerodynamics, and everything to do with the moment of inertia of the objects.
    // yummygooey

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    Quote Originally Posted by TejanoTrackie View Post
    . Finally, use the narrowest possible front rim and tire.
    Is this true? I know some of the newer Zipp rims are wide, and you use a narrow tire on them to create a leading edge or something to that effect.
    For example:
    http://www.zipp.com/technologies/aer.../firecrest.php
    Last edited by clink83; 01-27-11 at 09:43 PM.
    Quote Originally Posted by carleton View Post
    Dude, when you live by the Tarck sword, you die by the Tarck sword. Ashes to ashes and dust to dust.

  23. #23
    Veteran Racer TejanoTrackie's Avatar
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    Quote Originally Posted by clink83 View Post
    Is this true? I know some of the newer Zipp rims are wide, and you use a narrow tire on them to create a leading edge or something to that effect.
    Yeah, there's some newfangled aero stuff out there now where the rim kinda bulges out, but all the older wheels like the Mavic IO are very narrow, and designed to accept narrow tubular tires. I'm not really into the latest aerotech, and just use a Zipp 404 tubular front road wheel for all my TT stuff on the track and a narrowish 20mm tire.
    What, Me Worry? - Alfred E. Neuman

    Quote Originally Posted by Dcv View Post
    I'd like to think i have as much money as brains.

  24. #24
    Senior Member
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    Quote Originally Posted by yummygooey View Post
    I'm glad that you're trying to apply what you learn in class to real life, but you should do some more reading one why a solid disk will spin longer than a hoop. Your experiment probably had nothing to do with aerodynamics, and everything to do with the moment of inertia of the objects.
    hehe yep yep...

    university of illinois - urbana champaign physics professors FTW

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