How does improper rear-heavy weight distribution on a single-axle agricultural trailer affect vehicle combination stability?

1. It raises the load on the drawbar so far that the coupling is overstressed
2. It makes the combination more stable, because the mass sits closer to the trailer axle
3. It produces a negative tongue load that lifts the tractor's hitch, unloading the driven rear wheels and setting off snaking (Schlingern) that can end in a jackknife
4. It shortens the braking distance, because more mass sits over the braked trailer axle