A vehicle or machine suitable for operation on uneven or inclined surfaces, such as a forest work unit, comprises at least three frame parts and two rotational planes. Each frame part has rotational planes, in each particular case, on an interface between two successive frame parts of the vehicle or machine. The rotational planes are, in each particular case, planes perpendicular to the longitudinal axis of the vehicle or machine in the neutral position. The frame parts are thus arranged to be independently rotatable in relation to the rotational plane.