http://www.newstatesman.com/science/2013/08/we-still-don%E2%80%99t-really-know-how-bicycles-work
"[...] the gyroscopic effects are not enough to keep a bike upright after all. What does? We simply don’t know. Forget mysterious dark matter and the inexplicable accelerating expansion of the universe; the bicycle represents a far more embarrassing hole in the accomplishments of physics."