Help explaining physics demonstration

[Cardsfan06]

In my last class the professor had a bike tire with a string attached to its axle. When the tire was hung from the string it sat parallel to the floor; however, when it was spun and hung from the string it remained perpendicular to the floor and rotated around the string. What was it that kept the spinning wheel up?

. . . []. . . . . . . . . . . . . . . []
. . . []. . . . . . . . . . . . . . . []. @
. . . []. . . . . . . . . . . . . . . []. @
. . . []. . . . . . . . . . . . . . . []_@_
. . . .|. . . . . . . . . . . . . . . . . @
@@@@@@. . . . . . . . . . . . . .@
. . . .|. . . . . . . . . . . . . . . . . @

@ = tire
[] = string
| and _ = axle
. . = nothing
tire on right is the one spinning

 

[Mapes]

Its relatively large angular momentum (see http://en.wikipedia.org/wiki/Gyroscope" ).