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From 8 Simple Questions You Won't Believe Science Can't Answer:

  1. Bicycles have to designed by almost entirely by intuition and experimentation
  2. Physical concepts used to explain them (gyroscopic and caster effects) have been proven irrelevant

Articles like these choose a pessimistic/condescending attitude while stating this. What is the actual status, does science have a model to explain how bicycles balance themselves?

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Delft & Cornell University: TMS Bicycle, stable without gyros or trail (Video); The paper and supporting material can be found here –  Oliver_C Aug 9 '12 at 10:39
@Oliver_C thanks for that! –  aitchnyu Aug 9 '12 at 11:10
Cracked(the op's source) is noted(and I use that term loosely) for satire and humor... not scientific research. –  Chad Aug 9 '12 at 13:22
@Chad - However, Cracked does seem to note most of their sources for the claims in the article and it is presented in a humorous, but non-fiction fashion. –  rob Aug 9 '12 at 14:24
Bicycles don't balance themselves: left to their own devices they usually fall over quickly. Bicycles ridden by people find it easy to balance, but that is a much more complex system than just a bike and involves a great deal of feedback. The stability is far more a property of the feedback than the bike, so what is it exactly we can't explain? –  matt_black Aug 9 '12 at 17:04
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1 Answer

up vote 18 down vote accepted

Based on this paper (thanks to Oliver_C for posting it) you can quite clearly see that their behaviour is understood by physicists (they wrote a paper on it!)

To find the essence of bicycle self balance we looked at simpler and simpler dynamical models until we found a minimal two-mass-skate (TMS) bicycle that theory told us should be self-stable. This bicycle has no gyroscopic effect and no trail. We built a bicycle (of sorts) based on the theory to prove the point.

This shows that theory predicts their simple bike to be stable without gyroscopic or trail effects.

Gyroscopic forces and trail effects DO help bicycles remain stable, however. This paper just demonstrates that other effects are important too, and that bikes can be stable without gyroscopic forces or trail.

Why can a bicycle balance itself? One necessary condition for bicycle self stability is (once we define the words carefully) that such a bicycle turns into a fall.

This situation seems similar to that of aircraft, where the Bernoulli effect is often cited as being the cause of lift, while planes can fly without it (for example when they fly upside down, which some planes can do.) The gyroscopic effect certainly helps balance a bike, but isn't necessary, much like the Bernoulli effect helps give an aircraft lift but isn't necessary.

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that is more like explaining how bicycles don't work –  ajax333221 Aug 9 '12 at 17:47
The Bernoulli effect is not wrong - it just causes the kind of confusion you have. Check here. Simple inverted flight is -1G. A Cessna 172 is stressed for 1 +/- 3G. An Extra 300 is +/- 10G. The Extra has a symmetrical airfoil. The Cessna does not, only because it's not designed for aerobatics. –  Mike Dunlavey Aug 10 '12 at 12:26
@MikeDunlavey You can fly with a completely flat square wing though, the Bernoulli effect is a way to optimise efficiency. Lift comes from forcing air down, which happens when the air hits the lower edge of the wing and is deflected downward. –  Nick Aug 10 '12 at 12:38
You're right that lift (up or down) comes from deflecting the air stream. The role of Bernoulli is to provide the suction on the other side of the wing that makes the air follow the surface. If the air cannot follow the curve on both sides, the wing is much less effective at deflecting the flow. The term for that is a "stall", and there is a specific angle of attack at which it occurs, about 19 degrees. –  Mike Dunlavey Aug 10 '12 at 12:43
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