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  1. #1
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    Physics of Bicycles still .... witch craft

    Engineers disprove commonly held beliefs about the physics of bicycles

    Next time you ride your bike, you may want to take a moment to marvel at the complexity of the physics behind it. According to a recently published study, commonly-accepted explanations about the self-stability of bikes are actually false.

    Cornell mechanical and aerospace engineering professor Andy Ruina asserts that the science behind a bike's self-stability has been a mystery for well over a century. "A bicycle's not all that simple," Ruina affimed. "The mechanics of three-dimensional objects are complicated. In some sense, it's been well understood since the mid-1900s in that people can write the equations, but in terms of having some intuitive understanding of it, nobody ever has."

    The researchers first disproved formerly held beliefs about what contributed to self-stability, including gyroscopic motion and a design feature called "trail," which places the steering axis ahead of the front wheel's contact point with the ground. The team of scientists endeavored to build a bike that used neither of those features - and they were ultimately successful.

    Although the resulting bike, dubbed the two-mass-skate bicycle, lacks gyroscopic motion and trail, it does have handle bars that turn in the direction of the fall if the bike tips over. Ruina contends that while the research could seem trivial, it is indicative of bigger questions scientists still have no answers for.

    "Very little is known about how people do anything," he said. "We don't know how people walk; we don't know how people hold still; we don't know how people hold things. So one of the things to try to figure out is how people ride a bicycle and what about the bicycle makes it easy or hard to ride."
    yes, I know... I accidentally posted in the wrong forum
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  2. #2
    flinty-eyed moderator
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    moved per request
    Dr. Cox: Lady, people aren't chocolates. Do you know what they are mostly? Bastards. Bastard-coated bastards with bastard fillings. But I don't find them half as annoying as I find naive bubble-headed optimists who walk around vomiting sunshine.

  3. #3
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    They should devote their valuable research time to something more relevant to riders... like resolving the Campy vs Shimano argument

  4. #4
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    Quote Originally Posted by tednugent View Post

    ......but in terms of having some intuitive understanding of it, nobody ever has....
    I think this guy might beg to differ.

    * posted by Creakybot 2013 all rights reserved.
    * not actually waterproof.

  5. #5
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    Scary fast. I think those announcers need to back off the caffeine a bit

  6. #6
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    Quite fascinating. And to think we and all this physics and our ability to walk, talk, and ride a bike came from a big bang.

  7. #7
    Do what he say!
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    Physics of Bicycles still .... witch craft

    Quote Originally Posted by DaveG View Post
    I think those announcers need to back off the caffeine a bit
    He was either on blow or had money on him. Or both.
    I don't want to talk to you no more, you empty headed animal food trough wiper. I fart in your general direction. Your mother was a hamster and your father smelt of elderberries.

    No go away, or I shall taunt you a second time.

  8. #8
    Do what he say!
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    Physics of Bicycles still .... witch craft

    Quote Originally Posted by Creakyknees View Post
    I think this guy might beg to differ.

    Seats too low.
    I don't want to talk to you no more, you empty headed animal food trough wiper. I fart in your general direction. Your mother was a hamster and your father smelt of elderberries.

    No go away, or I shall taunt you a second time.

  9. #9
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    Those guys scared my son......and my boy loves LOUD.

    Off road tire technology has most certainly come a long way since my days on the single track. That and I'm sure that racer had a bit of skill.
    This mssg brought to you by Mr. Bananas.

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  10. #10
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    Misleading. The two-mass skate bicycle didn't 'disprove' that trail worked, it developed another method of achieving stability, by putting a weight well ahead of the front wheel, attached to the steering mechanism. If anything, it proves the dynamic fundamentals of how trail works, by showing an alternate geometry of the same effect.

    As for gyroscopic effect, no one ever thought that was a primary source of stability. We can argue all night whether it contributes at all, but the significance of it's effect is too small to matter.

    If trail didn't matter, it would be possible to configure a self-stable, rear-steering bike. That turns out not to work. .
    A good habit is as hard to break as a bad one..

  11. #11
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    Quote Originally Posted by danl1 View Post
    As for gyroscopic effect, no one ever thought that was a primary source of stability. We can argue all night whether it contributes at all, but the significance of it's effect is too small to matter.
    o.k., I'll go first; the gyroscopic effect is HUGE!
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  12. #12
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    Quote Originally Posted by metoou2 View Post
    o.k., i'll go first; the gyroscopic effect is huge!
    tiny!
    A good habit is as hard to break as a bad one..

  13. #13
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    your arguments are iron clad and I can now see your side of it............
    "tiny"!
    I will back your, (our) position and fight all those opposed to the death.
    This mssg brought to you by Mr. Bananas.

    Shouldn't it be called a 'nipple wrench'?

  14. #14
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    Quote Originally Posted by danl1 View Post
    As for gyroscopic effect, no one ever thought that was a primary source of stability. We can argue all night whether it contributes at all, but the significance of it's effect is too small to matter.
    Actually some people did make this argument. There was a famous bike built with a second set of wheels attached that could be spun in the opposite direction of the actual wheels so as to cancel the gyroscopic effect and prove that the bike was stable without it. It could be argued that those with engineering/physics understanding didn't think gyroscopic effects were important (and of course knew how to demonstrate it) but think of all the physics falsehoods that are regularly posted here by those who just "know" what's right.

  15. #15
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    I gotta see that.............please tell me you have a link.
    This mssg brought to you by Mr. Bananas.

    Shouldn't it be called a 'nipple wrench'?

  16. #16
    warrrrrrrgh!!!
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    I think the point the author made is that bicycle physics are understood, but what exactly it is about a bicycle that makes it sweet to ride still is unknown.

    Thus we still have a lot of experimenting with geometries, wheel sizes, suspension designs etc. People have an intuition as to what feels good and how to ride fast, but not what the perfect bike would be.

    BTW, this guy wrote my Freshman dynamics text book.
    I hate you all

    j/k lol kthxbye!

  17. #17
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    Quote Originally Posted by Creakyknees View Post
    I think this guy might beg to differ.

    That's a cool video you have of me.
    ”Nothing sucks more than that moment during an argument when you realize you’re wrong” - Unknown

  18. #18
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    Quote Originally Posted by Creakyknees View Post
    I think this guy might beg to differ.
    That was an awesome ride.
    I hate you all

    j/k lol kthxbye!

  19. #19
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    Is the two-mass-skate bicycle laterally stiff yet vertically compliant? And can I get it with UCI approved disc brakes?

  20. #20
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    Quote Originally Posted by Creakyknees View Post
    I think this guy might beg to differ.

    ...lol the closing comment "how does the guy sit down with balls that big"....

  21. #21
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    If bicycle physics is witchcraft, what's unicycle physics?
    ... 'cuz that's how I roll.

  22. #22
    irony intended
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    Quote Originally Posted by looigi View Post
    If bicycle physics is witchcraft, what's unicycle physics?
    Mormonism...
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  23. #23
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    Quote Originally Posted by MrMook View Post
    Is the two-mass-skate bicycle laterally stiff yet vertically compliant? And can I get it with UCI approved disc brakes?
    Does Trek make good two-mass-skate bikes?
    "It ain't a teacup that the Queen gave you - it's a bike. Ride it!"

  24. #24
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    Quote Originally Posted by metoou2 View Post
    I gotta see that.............please tell me you have a link.
    I'll have to let you search for a video. The work was done in the late 1960s and so any images would be stills or home movies. See Jones, David E. H. (1970). "The stability of the bicycle". Physics Today 23 (4): 34–40.

  25. #25
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    Quote Originally Posted by Kerry Irons View Post
    Actually some people did make this argument. There was a famous bike built with a second set of wheels attached that could be spun in the opposite direction of the actual wheels so as to cancel the gyroscopic effect and prove that the bike was stable without it. It could be argued that those with engineering/physics understanding didn't think gyroscopic effects were important (and of course knew how to demonstrate it) but think of all the physics falsehoods that are regularly posted here by those who just "know" what's right.
    I think it was long accepted that it was a contributor to stability. And it can provide a 'sense' of stability by providing a damping action to front wheel steering motion. That actually works against 'real' stability, but it adds to the perception of it (compare riding a small-wheel folder to a standard bike for a view of the perception.)

    I've never seen an academic sort of argument trying to hold that it was 'the' major contributor to stability. That's all I was trying to say. Of course you are right that it's long been disproven to be a fundamental part of bicycle stability.
    A good habit is as hard to break as a bad one..

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