this site explains centripetal motion. I believe we all should have been saying centripetal all along. not centifugal.
http://www.glenbrook.k12.il.us/gbssc...rcmot/ucm.html
the reason your tire flies off the wheel is because centripetal force loosens the tire's grip on the wheel, thus making it free to move. some other force (ie friction, slight angle, air, imperfections in the surface of the tire) actually makes the tire leave the rim.