A wheel unit mountable on a ski of a ski-mounted vehicle includes an actuating plate defining a wheel attachment section and a piston attachment section The actuating plate is pivotally attached to the ski intermediate the wheel and piston attachment sections for pivotal movement about a plate pivotal axis. A wheel attachment assembly is provided for rotatably attaching the wheel to the wheel attachment section. An actuator is operatively coupled to the actuating plate for selectively pivoting the actuating plate about the plate pivotal axis between a plate deployed configuration and a plate retracted configuration wherein in the plate deployed configuration the position of the actuating plate is such that the wheel protrudes at least partially below the ski gliding surface for engaging the ground surface and in the plate retracted configuration the position of the actuating plate is such that the wheel is retracted above the ski gliding surface for preventing the wheel from engaging the ground surface. A plate transversal moving assembly is operatively coupled to the actuating plate for selectively moving the actuating plate substantially transversally relative to the ski.