Always in the tire track and almost always in the left one unless I'm riding with other motorcycles in the aforementioned staggered positions.
Originally Posted by billbunton
As to 'why', several reasons have already been stated and, in fact, the Motorcycle Safety Institute's guidelines... which have been adopted by many states as part of their motorcycle training / licensing curriculum -- includes things like the following:
Because of a motorcycle’s size, its position within a lane of traffic will change
as traffic conditions change.
THE MOTORCYCLIST should choose a position in the lane to be seen.This
often means you will ride in the left portion of a traffic lane.This position
gives him/her a better view of traffic and the road ahead, as well as making
the motorcycle more visible to other traffic in most situations.
As a motorcyclist, you should change position within your lane as needed to
maximize distance from potential hazards. Lateral movements within a lane
may be necessary at times to increase your chance of being seen.Avoid riding
for any length of time in a driver’s blind spot. Experienced riders realize that
the best position within a lane of traffic is dictated by the situation.
Same thing goes for Group Riding: http://www.msf-usa.org/downloads/Group_Ride.pdf
As an example, these MSF guidelines have ended up in Georgia's Motorcycle Handbook: http://www.dds.ga.gov/docs/forms/MotorManual.pdf
P. 13 = Lane Position
P. 35 = Group Riding