Brake control for a vehicle system configurable as a tractor with an articulatable semi-trailer or as a tractor with a non-articulable semi-trailer

A tractor brake system includes a brake control unit (106) connected to brake actuators of the tractor (1) for controlling brake effort caused to be exerted by the brake actuators (82, 88) and at least one coupling member (C1) for coupling a semi-trailer brake system of the rigidly coupled semi-trailer (2) to the tractor brake system. The brake control unit (106) is adapted for controlling brake force distribution between brakes (83, 89) of axes (3, 4) of the tractor (1) according to at least a first control mode and for controlling brake force distribution between brakes (83, 89) of axes (3, 4) of the tractor (1) according to at least a second control mode and for operation in the second control mode in response to presence of the rigidly coupled semi-trailer (2).