A for 2 reasons. If you are in the left side of the lane when you begin the pass you have the best view for safety and oncoming traffic. You only move from the left of your lane to the right side of the oncoming lane then back to the left side after the pass. Shortest distance possible if you think about it. Once you have taken the lane you have an opportunity to view behind you and see the traffic in the rear including the other motorcyclists. You have an opportunity to signal as well as note when the other motorcyclists are coming. We traditionally stay to the left of the lane until they start to pass then we will move to the right to allow the passing bike to take the lane then we will move back into the left lane and the bike(s) behind us move to a staggered position again for safety allowing the ride leader to see all the bikes behind him. # 2 staggered formation can help should one bike go down theres a chance they make be able to take corrective action and all the bikes don't have to go down.