This disclosure relates to a wheel assembly (1) comprising a wheel, the wheel having a hub and a rim concentrically mounted to the hub, a plurality of deformable chambers (6) disposed outwardly of the rim, each chamber extending about a discreet portion of the wheel and containing a transition substance (15), and an actuator (14) configured to transform the transition substance (15) within each chamber (6) between a fluid state in which the deformable chamber (6) can deform into a conformal state as the wheel encounters an obstacle during use, and a rigid state in which the transition substance is rigidified to maintain the deformable chamber (6) in said conformal state to provide increased purchase on said obstacle.
