A swather tractor has a frame defined by a main tractor frame carrying the cab, engine and drive system, rear axle with castor wheels and a transverse front frame assembly mounted at a front of the main frame. The front rigid frame assembly carries the header and comprises a cross member and a pair of upstanding legs each carrying a front ground wheel hydraulically driven so that steering is controlled by the rate of forward movement of the front wheels. In order to provide improved suspension, the main frame is connected to the front frame assembly by a coupling which allows up and down suspension movement of the main frame relative to the front frame assembly.