Tractor-Trailer Turning, Tracking, and Off-Tracking
Tractor-Trailer Turning, Tracking, and Off-Tracking tests the geometry of a turn: where the rear wheels actually go, where the trailer's tail swings, and how to set up a turn so nothing and no one is crushed.
The geometry
- Off-tracking: the rear wheels of the tractor and the trailer's wheels follow a path inside the front wheels. The longer the wheelbase and the sharper the turn, the wider that gap.
- Swing-out: during a turn, the rear of the tractor and the rear of the trailer swing toward the outside of the turn. In a right turn, the tractor's rear overhang swings left while the trailer's tail swings too.
- Rearward amplification: with doubles and triples, each unit amplifies the steering input, so the last trailer's path is wider and can intrude into the next lane.
Rules for turns
- Start in the correct lane. Do not swing wide before the turn - that opens a gap on your right and invites a car into it.
- Pull forward into the intersection, then swing wide as you complete the turn.
- Watch both mirrors through the turn; the right mirror shows the trailer's right rear wheels cutting toward the curb.
- Take the whole lane and accept a wide path rather than clipping a curb, pole, or pedestrian.
- Back toward the driver's side whenever possible, with a helper and agreed hand signals. If you cannot see, get out and look.
Worked example
A 70-foot rig turns right from a four-lane road into a three-lane road. The driver stays in the right lane, pulls forward until the tractor's rear wheels are near the far curb line, then swings wide while watching the right mirror. The trailer's right rear wheels track roughly a lane inside the tractor's front wheels; had the driver started the turn early from the left lane, the trailer would have cut the corner and struck the curb or a pedestrian waiting there.
Traps
- Swinging left before a right turn.
- Cutting the corner and assuming the trailer will follow.
- Forgetting the outside swing of your own rear overhang, which clips signs and parked cars.
- Backing to the blind side without help.