That's why I work with two, one on the helmet, one on the bars. The inner tube method doesn't move from how every I adjust it. I like to make it tight so when I go off road (with no suspension) and the light stays pointing where I intended it to point, straight on.

The beauty of the inner tube method is, it's free, it stays securely attached on all terrain, no worries if you leave the tube on the bike when parked, it's FREE (take flashlight), and easy removal of flashlight. One that many may not notice, it's subtle but protects the light, the bar on the bike and eliminates noise from the flashlight hitting the bar on rough terrain. It's the fact the tube is fully wrapped around the handle bar, isolating the flashlight from the handle bars. This prevents the light from moving at all, as said before, on any road condition.