Advantages/Disadvantages of "hanging off" a motorcycle when leaning The closest question I could find with regards to this subject was this one:
Countersteering a motorcycle
However, it does not address the specific physics of what I would like to know.
There are 3 ways to lean when turning a motorcycle:


*

*Upper body remains upright while the bike leans.

*Whole body remains aligned with bike.

*Most of the body "hangs off" the side leaning in.


I'm trying not to make any assumptions to allow for detailed and proper answers addressing issues I may not have considered; hopefully, without being too generic.
So to summarize, I would like to know whether the first 2 items are sufficient for all conditions or whether the 3rd has some physical properties necessary in certain conditions.
 A: The point of lean is to keep the center of mass aligned with the force vector which sums gravity (purely perpendicular to the horizon) with the acceleration forces created by the turn. Traveling in a straight line, the only force is gravity, so you center yourself upright over an upright bike. As you initiate a turn, you lean at some angle; the more aggressive the turn, the greater the angle from vertical. At some point, you will either exceed the limits of the tire's grip, or some part of the bike will contact the ground. In either case, the most likely outcome is a spill.
If you have very grippy tires, the limit of the bike's lean could will be interference with the road from some part of the bike. That's when the rider would want to hang off the bike - to increase the effective lean of the bike i.e. move the center of mass further - without a further increase in lean of the bike.
Apart from bike part contacts road, another consideration may be the design of the tires and the geometry of a sharply inclined rotating tire on the road;  that the tire tread may no longer be simply planting itself on the road but squirming around. If that is happening, one would expect a few not-so-nice things to go along with it - wasted energy, wear on the tire, loss of effective grip because of opposing forces, and loss of grip because static friction between tire and pavement has been replaced by dynamic friction.
A: All the force to accelerate or turn a motorcycle come from the wheel/ground interface.  So to turn a bike quickly means a larger force on the wheel (from friction on the ground).
If the bike were upright when a strong sideways force were applied, it would quickly rotate the bike around its center of mass and dump the rider.  Instead, the rider leans into the turn so that the sum of the friction and normal forces go through the center of mass and there is no torque to flip the bike.
The harder the turn, the more the center of mass must be displaced from the vertical.  So the hardest turn possible would be limited either by the static friction of the tires, or by the amount the center of mass could be displaced.  Hanging off allows for greater displacement.
A: The important thing about leaning in is that it puts you closer to the road so you don't have so far to fall when you exceed the stickiness of your tires.
