Why does a bicycle wheel precess when suspended from a string?

[Amith2006]

Almost everything is clear to me as far as the reason for the precession of a bicycle wheel suspended by a string from a rigid support is concerned. But I don't understand one thing about it. There are 2 forces acting on the system- one is the downward force of gravity at the center of mass of the wheel and the other is the tension in the string acting in the upward direction. It is said that the axle of the wheel manages to remain horizontal as the 2 forces get cancelled. How is it possible when the lines of action of the 2 forces are different?

 

[Dale]

The lines of action affect the net torque, but not the net force.

 

[Amith2006]

You are right! Thanx.