Abstract: A mobile belt support car for a conveyor system having an extensible conveyor belt which includes a troughing strand and a return strand. Each car of a mobile support structure includes a longitudinal frame having first and second opposite axial ends, first and second horizontally pivoting joints provided respectively at the first and second opposite axial ends of the longitudinal frame, a transverse beam fixedly connected to the longitudinal frame and having first and second opposite axial ends, first and second wheels supported respectively at the first and second opposite axial ends of the transverse beam, and a first idler frame assembly mounted on the longitudinal frame and including an upper cantilevered beam, a lower cantilevered beam, the first and second cantilevered beams extending towards the extensible conveyor belt, and upper rollers, mounted on the upper cantilevered beam, for supporting the troughing strand of the extensible conveyor belt.