Handling Curves, Turns, and Offtracking
The geometry of a long combination
Every turn in a multi-trailer rig is a geometry problem. The tractor's front wheels follow one path, the drive wheels a tighter one, and each trailer behind tracks further inside. This is offtracking, and it grows with each added unit. The total width the combination sweeps is the swept path, and it must fit within the lane or the turn.
Concepts to name
- Offtracking: rear wheels track inside the front wheels' path.
- Swept path: the full width needed through a turn, including the rear trailer's swing.
- Turning radius: multi-trailer rigs need a wider turn than a single trailer.
- Right turns: swing wide to the left before turning right, but watch for vehicles beside you.
- Left turns: do not cut the corner; the rear trailer will track inside and may strike the curb or a pole.
- Curves: enter at a safe speed; braking in a curve is dangerous because it can cause a skid.
Common traps
Questions often suggest that because the rear trailer tracks inside, you should turn later - the opposite is true; you must start the turn wider and later to keep the rear trailer clear. Another trap is assuming offtracking is the same for left and right turns; the swept path differs.
Rule of thumb
On a tight right turn, pull forward until your tractor is past the corner, then swing wide and turn slowly, checking mirrors for the rear trailer's path.