腳踏車為什麼可以保持直立？

How does a bike stay upright? Surprisingly, it’s all in the mind

http://theconversation.com/how-does-a-bike-stay-upright-surprisingly-its-all-in-the-mind-59829

Bicyles are not held up by the gyroscopic effect

http://www2.eng.cam.ac.uk/~hemh1/gyrobike.htm

A Bicycle Can Be Self-Stable Without Gyroscopic or Caster Effects

http://science.sciencemag.org/content/332/6027/339