This disclosure relates to a wheel assembly (1) comprising a wheel, a deformable chamber (6) containing a transition substance (15) comprising jamming particles and an interstitial gas, and an actuator (14) configured to transform the transition substance (15) 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 by evacuation of the interstitial gas in which the transition substance is rigidified to maintain the deformable chamber (6) in said conformal state to provide increased purchase on said obstacle.
