What is off-tracking and how does it affect large vehicles making turns?

OFF-TRACKING (also called CHEATING) is the geometric difference between the path of the front (steering) wheels and the path of the rear wheels when a vehicle makes a turn. For a standard car, off-tracking is small and mostly unnoticeable. For a 53-foot tractor-trailer, it is dramatic and dangerous. HOW IT WORKS: The front wheels follow an arc on the outside of the turn. The rear wheels, attached much farther back, follow a SHORTER arc on the INSIDE of the turn. The degree of off-tracking increases with: (1) Longer vehicle (more distance between steer axle and rear axle); (2) Tighter turn radius; (3) More articulations (a double 53-footer has worse off-tracking than a single). REAL-WORLD CONSEQUENCE: On a right turn from a two-lane road, a tractor-trailer's rear wheels may track over the curb, into a bicycle lane, or over pedestrians in the crosswalk — even if the driver began the turn from the correct position. CORRECT TECHNIQUE: 'Button hook' or swing wide before the turn — steer slightly left before turning right to create space for the rear to track; watch the mirrors to monitor where the rear wheels are going; be aware that pedestrians standing on the corner are in your rear path even if they're clear of the front; never turn from the wrong lane.