Why are empty trucks/trailers sometimes more difficult to stop safely than loaded ones?

EMPTY VEHICLE BRAKING: Counterintuitively, empty trucks and trailers can require GREATER stopping distances and are more prone to wheel lockup than properly loaded ones. WHY: Less weight means less traction (less force pressing the tires onto the road); the braking system is designed to stop a heavily loaded vehicle, so on an empty vehicle the brakes can be too powerful relative to the available traction, causing the wheels to LOCK UP and SKID; locked wheels = loss of control and longer stopping distance; bouncing of the lightly loaded axle reduces tire-road contact; IMPLICATIONS: Empty vehicles are more prone to jackknife and skidding; drivers must brake gently and allow more following distance; some trailers have load-sensing or anti-lock systems to help; this is a frequently tested and counterintuitive concept — many assume empty = easier to stop, but the traction issue makes empty vehicles handle and brake differently; adjust driving for the load (or lack of it).