A harvesting header on a vehicle such as a combine harvester includes a mounting assembly comprising left and right float elements each for applying controlled left and right lift forces and arranged to allow upward floating of each end of the header in response to ground contact. Left and right sensors detect the angle of tilt of the header and a control system operates to reduce the left lift force when the left end is raised and to reduce the right lift force when the right end is raised. On a combine harvester this can be done by rotating the face plate of the feeder house in the required direction. In other systems the force generated by the left and right float elements can be directly modified. The changes to the lift force are applied only when the propulsion vehicle is tilted beyond a predetermined angle.
