Offtracking, Rearward Amplification, and Other Handling Hazards
Offtracking, Rearward Amplification, and Other Handling Hazards
This domain tests the physics that make long combinations dangerous: offtracking, rearward amplification, rollover, sway, and the effect of speed and load. The exam asks you to predict where the trailer will go and how multiple trailers amplify motion.
Definitions
- Offtracking: the rear wheels of a vehicle follow a tighter path than the front wheels in a turn. The longer the wheelbase and the sharper the turn, the greater the cut.
- Rearward amplification: in doubles and triples, a steering movement at the tractor grows larger at each trailing unit. The last trailer can swing widest.
- Rollover: high center of gravity plus lateral acceleration. Speed in a curve is the main driver.
- Sway: oscillation caused by steering, load, or speed; it can grow into a loss of control.
Core rules
- Slow down before curves; do not brake hard in the curve.
- Steer smoothly; small inputs, not sudden corrections.
- Load heavy items low and centered.
- Check tire pressure and suspension.
- Give extra room at corners, fuel islands, and toll booths.
- In doubles and triples, the last trailer's swing is the widest.
Worked example
A triple-trailer unit enters a curve at the posted speed for cars. The driver feels the last trailer swing outward. The correct action is to ease off the accelerator smoothly and make small steering corrections, not to brake hard or jerk the wheel. Rearward amplification means the last trailer's lateral movement is larger than the tractor's; adding hard braking can trigger a rollover or jackknife.
Traps
- Treating the posted car speed as a truck speed.
- Braking hard in a curve.
- Loading heavy cargo high.
- Assuming the last trailer tracks the first.
- Correcting sway with a sharp steer.
Key points
- Offtracking increases with length and turn sharpness.
- Rearward amplification grows toward the last trailer.
- Slow before curves; smooth steering.
- Load low and centered.
- Give long units extra clearance.