Motorcycle rider postures

The motorcyclist's riding position depends on rider body-geometry (anthropometry) combined with the geometry of the motorcycle itself — falling along a spectrum of three basic postures.[29]

* Standard: In this position the rider sits roughly upright, in a neutral position, neither leaning forward nor rearward, knees lower than the hips, and feet roughly below the riders centre of gravity. The rider has excellent visibility and a higher seat height—but with greater wind resistance, a higher centre of gravity, and potentially more difficulty flat-footing—having the ability, when stationary, to put both feet flat on the ground for safety and comfort, keeping the machine upright.

* Sport: In this position the rider leans forward with the upper torso, supporting the upper-body weight with the back, stomach and leg muscles thereby keeping the forearms loose and relaxed providing smooth steering input/feedback at the handlebars. Knees are at hip height or below and squeezed against the tank to help support the upper body with the feet positioned on the balls of the foot on the footpegs. The position offers the advantage of decreased wind resistance but an otherwise cramped position that may be difficult to sustain for longer periods (some hours). The Sport riding position offers good flat-footing.

* Cruiser: In this position the rider sits at a lower seat-height with the upper torso upright to slightly rearward. Knees are near hip height and legs extended forward. This position offers the advantage of comfortable circulation to the legs and ease of flat-footing—though with a lower field of visibility. In this position the rider may have difficulty lifting off the seat (when crossing an obstacle for example).

Important factors of a motorcycle's ergonomic geometry that determine the seating posture include the height, angle and location of footpegs, seat and handlebars. Likewise, factors in a rider's physical geometry that contribute to seating posture include torso, arm, thigh and leg length, and overall rider height.
From: http://en.wikipedia.org