A detachable header for a self-propelled agricultural working machine comprising at a front of the machine a feeder configured to be moved up or down, and said header that is detachably coupled to a front of the feeder, wherein the header comprises a back wall and two support and transport wheel assemblies (11,12) on either side of the feeder, designated as front and rear wheel assemblies, the front and rear wheel assembly each comprising an axle and two wheels (14a, 14b) attached at the two ends of the axle, the assemblies being movable between a field position wherein the axle is parallel to the longitudinal direction of the header and a transport position wherein the axle is transversal to said longitudinal direction, and wherein the front wheel assembly comprises: • a pivotable base that is pivotably connected to a central location of the axle of the front wheel assembly, the base being pivotable about a vertical axis, • a first tie rod arrangement (62a, 62b; 80, 81) configured to transfer the pivotal position of the base to the wheels (14a, 14b) of the front wheel assembly, characterized in that: - the header further comprises two actuating systems configured to move the wheel assemblies from the field position to the transport position and vice versa, - the wheels (14a,14b) of the wheel assemblies (11,12) are pivotable relative to their respective axles and about axes which are transversal to said axles, in order to steer the wheel assemblies, - the front wheel assembly further comprises: • a first variable length actuator pivotably coupled to the axle of the front wheel assembly and to one of the wheels of said front wheel assembly, and - the rear wheel assembly comprises: • a second tie rod arrangement (69;83a,83b) configured to transfer the pivotal position of one rear wheel to the other rear wheel, • a second variable length actuator pivotably coupled to the axle of the rear wheel assembly and to one of the wheels of the rear wheel assembly, - the first variable length actuator is hydraulically coupled to the second variable length actuator, wherein the hydraulic coupling between the actuators is configured so that the extension of the first variable length actuator results in the retraction or the extension of the second variable length actuator, such that the operation of the variable length actuators (66,68) of the front and rear wheel assemblies is synchronized, so as to synchronize the actions of the first and second variable length actuators (66,68) and thus the pivotal positions of the wheels of the front and rear wheel assemblies (11,12). • a pivotable base that is pivotably connected to a central location of the axle of the front wheel assembly, the base being pivotable about a vertical axis, • a first tie rod arrangement (62a, 62b; 80, 81) configured to transfer the pivotal position of the base to the wheels (14a, 14b) of the front wheel assembly, - the header further comprises two actuating systems configured to move the wheel assemblies from the field position to the transport position and vice versa, - the wheels (14a,14b) of the wheel assemblies (11,12) are pivotable relative to their respective axles and about axes which are transversal to said axles, in order to steer the wheel assemblies, - the front wheel assembly further comprises: • a first variable length actuator pivotably coupled to the axle of the front wheel assembly and to one of the wheels of said front wheel assembly, and • a first variable length actuator pivotably coupled to the axle of the front wheel assembly and to one of the wheels of said front wheel assembly, and - the rear wheel assembly comprises: • a second tie rod arrangement (69;83a,83b) configured to transfer the pivotal position of one rear wheel to the other rear wheel, • a second variable length actuator pivotably coupled to the axle of the rear wheel assembly and to one of the wheels of the rear wheel assembly, • a second tie rod arrangement (69;83a,83b) configured to transfer the pivotal position of one rear wheel to the other rear wheel, • a second variable length actuator pivotably coupled to the axle of the rear wheel assembly and to one of the wheels of the rear wheel assembly, - the first variable length actuator is hydraulically coupled to the second variable length actuator, wherein the hydraulic coupling between the actuators is configured so that the extension of the first variable length actuator results in the retraction or the extension of the second variable length actuator, such that the operation of the variable length actuators (66,68) of the front and rear wheel assemblies is synchronized, so as to synchronize the actions of the first and second variable length actuators (66,68) and thus the pivotal positions of the wheels of the front and rear wheel assemblies (11,12).