When loading heavy cargo on a semi-trailer, what dangerous physical phenomenon occurs if the cargo is positioned too far to the rear behind the trailer axle group?

1. The fifth-wheel coupling load (Sattellast) on the tractor's drive axle is excessively reduced, diminishing drive axle traction and causing steering instability or trailer jackknifing
2. The steering axle of the tractor becomes overloaded
3. The trailer kingpin breaks instantly from excessive downward vertical force
4. Fuel consumption decreases by 30% due to aerodynamic tail lift