I don't quite understand WHY a gyroscope precesses the way it does. I'll set up an example in order to ask the questions I need. Lets say you have a spinning bicycle wheel suspended at one end of its hub by a string. Due to the angular momentum of the spinning wheel, the wheel will precess about an axis parallel to the string. I understand that the wheel has an angular momentum vector parallel to the axis the wheel spins about (horrizontal). And I understand that the weight of the wheel produces a torque vector that is orthogonal to the axis of rotation of the wheel. What I don't understand is how the torque vector pointing in this direction causes precession about the string. I don't see how a torque can cause rotation about an axis oriented 90 degrees away from the torque vector. Once the wheel starts to precess about the string, the momentum vector changes position and rotates about the string along with the axis of rotation of the wheel. How does this motion not violate the principal of conservation of angular momentum when the movement of the rotation axis downward does?