FRONT END SHAKE
I agree with the tire internal problem...not noticed till you get it rotating to a certain speed. First though, stand over the bike and hold the front brake to keep the bike from rolling and try to push and pull the bike back and forth to see if anything is wrong visually...you shouldn't see anything move from side-to-side or feel anything other than the front forks smoothly compressing and expanding...IF you do then you have a problem somewhere in the front end...but MY money would be on the tire. I had a problem with an old Honda 450 (okay, real long time ago) but even on the centerstand and someone settong on the bike holding the back end down, you could spin the front tire and not see ANY freeplay, or any deflection from the sidewalls or tread. We decided to blow the tire way up, because the front end seemed ok and the tire was slightly worn anyway, to 50PSI...and then you could see some deflection...I DO NOT THINK THAT THIS IS A GOOD IDEA....DANGER>>>DANGER...You could mess up more than a rim, and even get hurt doing this! I'd buy a new front tire, a tire that you really would put your life on...really!