Abstract: A rotary mower having a central section and extension wings or end sections relatively pivotably movable upwardly and downwardly with respect to the central section. Each of the sections includes a plurality of cutting units mounted for rotation about vertical axis to provide a horizontal cutting plane across the width of the mower when the extension wings are in a lower or mowing position. Each cutting unit is carried on a horizontally disposed pneumatic tire wheel. An external drive rotates one of the tire wheels. The other tire wheels are mounted in frictional circumferential engagement with each other and the driven tire wheel so that all wheels are driven in the mowing position. When either of the extension wings is pivotally raised to a position greater than approximately 30.degree. relative to the center section, its tire wheels are moved out of frictional engagement with the tire wheels of the center section so that its cutting units are rendered inoperable.