What is the primary danger when driving an empty semi-trailer (bobtail tractor or empty flatbed) compared to a fully loaded truck?

1. Light weight provides less tire friction, causing wheel lockup, bouncing, extended braking distances, and extreme vulnerability to strong crosswinds
2. The truck cannot climb hills when empty
3. The engine overheats because there is no cargo to absorb heat
4. Empty trailers cannot be steered around corners