It was on a very high speed descent, 50-60mph on a very very steep grade in Utah on a bike with steel wheels where I felt the vibration. They were well trued, but it was porbably the cheap kenda tires and old, old well used steel rims just weren't well balanced I'm sure. I've never had a problem with anything aluminum, or with Chicago Schwinn steel wheels, s-6(schwinn proprietary 26") or s-7(27") at high speeds.