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Although I can’t say I’d care to try, or can in good conscience recommend, that trick where you let go of the handlebars at speed and sit upright in the saddle with your hands at your sides, this video from Ira Flatow’s Science Friday helps explain why it works. [Thanks, Laura!]

Sean Michael Ragan

I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I write for MAKE, serve as Technical Editor for MAKE magazine, and develop original DIY content for Make: Projects.


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Comments

  1. Anonymous says:

    From the video we appear to learn: the reason bikes are stable are not gyroscopic (torque) and not (steering) trail; a model is built that is stable(ish) without those two. That leaves us with …a mystery? (kind’ve of Sopranos ending) Is the answer in the paper? if so, could we have a link to this paper that reveals all?

    1. Anonymous says:

      The pdf is here:
      http://arxiv.org/PS_cache/arxiv/pdf/1009/1009.5574v1.pdf

      The cliff note version (as I understand it) is that the mass at the rear wheel moves more slowly than the mass at the steering mechanism, so that as the bike leans, the tendency is for the bike to turn “into” the turn faster than the mass can fall, resulting in stability above certain speeds.

  2. Anonymous says:

    I agree. However, the article currently resides behind a pay wall (shakes head). If you are interested in reading more you can see another paper dealing with the same by Jim Papadopoulos at
    http://ruina.tam.cornell.edu/research/topics/bicycle_mechanics/stablebicycle/StableBicyclev34Revised.pdf

  3. Ben Zaslow says:

    http://www.wired.com/wiredscience/2011/04/moving-bicycle-physics/

    “Attempts to understand this stability have been around almost for as long as bicycles have existed, and most people have accepted explanations focused on gyroscopic forces and the location of the steer axis. But a team of engineers has now built a bicycle that eliminates both of these features, but still manages to stay upright.”

  4. Dave Brunker says:

    What happens if you put a bicycle on a treadmill at the gym? Will the belt cause the wheels to spin and keep the bike upright from gyroscopic torque?

    1. Intuitively I would say no, because there is no forward momentum to help keep the lateral balance.

    2. Alan says:

      It should. Google “bicycle rollers” and you’ll find that while training, competitive cyclists routinely balance on bikes that are going nowhere. A treadmill would presumably work the same way, though it would be harder to keep things stabilized – you’d have to regulate your speed very carefully to avoid flying off the front or back of the belt.

  5. once i saw this exact same question in a physics riddles book.
    we discussed it with my friend a while.
    it was based on angular momentum as far as i can remember

  6. dj_nme says:

    I can see 4 wheels that would give gyroscpoic stability to the weird thing in the video.
    4 gyros (2 wheels, plus 2 gryos) are more stable than 2 gyros (2 wheels).
    It is obvious just looking at it.

    Gyroscopic stablisation hasn’t been disproved.

    1. those wheels are too small and spinning too slowly for gyroscopic forces to have anything to do with the stability of the bicycle.

      1. Anonymous says:

        That, and they’re counter-rotating. Which makes gyroscopic forces go from negligible to exactly zero.

  7. Anonymous says:

    A while back, Make featured a few oddball bikes. One with a hinged seatpost (rear wheel steering) and one with a pair of gears linking the handlebars to the fork. On that one, a left turn on the handlebars made the wheel turn right. If I recall, they said this bike was almost completely un-ridable. Anyway, this paper probably partially explains why. The weight shift would turn the wheel the wrong way! It’s the opposite of stable – even without the rider.

  8. Geo Shaw says:

    i’m not an engineer or a physics professor, but it would it would seem that there would ALWAYS be a part of a wheel that does the steering and a part that does the trailing, no matter what it was made out of or how minute it is.