When turning a tractor-trailer, why must you swing wide?

Off-tracking is the geometric tendency of the trailer's rear wheels to follow a tighter path through a turn than the tractor. On a right turn, if you steer tight to the inside curb, the trailer's rear wheels will climb the curb or strike pedestrians and vehicles on the inside corner. The technique is to begin the turn from further out (without crossing into oncoming or adjacent lanes), aim to put the tractor's rear wheels close to the corner you are turning around, and let the trailer's wheels follow the tractor's wheels through the turn. Off-tracking is greater with longer trailers and tighter turns. Drivers must learn to feel where the rear of the trailer is at any moment during a turn, since it is invisible in the mirrors during much of the maneuver.