Here's another angle to gyroscope theory as it applies to a bicycle:

While riding no hands on the handlebars, sometimes the front wheel will begin wobbling ryhtmically which may become violent and dangerous if allowed to grow.

Now I have not seen this anywhere else, not even with Jobst Brandt's or Sheldon Brown's stuff, but I am convinced this is due to nutation, a phenomenon observed in spinning rigid bodies.

You can observe this by taking a bicycle wheel, spinning it up while it is suspended by a string or even by hand, and giving the tyre a bump parallel to the axle. The wheel will begin to oscillate, and the rate of oscillation depends on the angular momentum, ie the wheel's angular moment and rotational speed. Nutation is a second order harmonic motion, damped only by external influences, so it can be initiated very easily and carry on for long.

A bicycle wheel is always subject to various perturbations from the road, wind and rider; if you ride no hands and at sufficient speed, the wheel's nutation frequency will start to coincide with the bicycle's and rider's overall geometry and distributed inertia's tendency to wobble, and the result is the front wheel starts to wobble.