Once made the mistake of diverting through Yellowstone on our way home and it was the week before Sturgis. Legions of RVs pulling trailers with HDs and HD clones in every camp ground. In the morning they would swarm into groups of 20-50 bikes and parade around the park at 10-15 MPH under the speed limit. They of course were in T-shirts, shorts and sandles and cared not the least little bit about the impact of their behavior on others. Not a day to expect to see wildlife. What is amazing is that they seem to think that other people are looking at them with admiration when in fact it is the look of distaste for their inconsiderate passive aggressive behavior. The OP is wise to try to avoid any event that causes the area to become infested with large numbers of such riders.