zzzwillzzz is right siulon. Nothing personal, it's just that by your own admission you don't want to cause a mishap by your lack of pack riding experience. If you are riding half the speed of those people, many of which are training for competitive events, and you find it unnerving when they pass, you are an obsticle in the path which requires the pack to accomodate your presence. That alone can result in a mishap within the ranks because someone isn't expecting the change in movement to make that accomodation. Join in some less demanding rides to gain experience and ability, and enjoy the ride.