Abstract: A wheel assembly for a rail vehicle that travels on a rail; the wheel assembly comprising a wheel axle, a wheel and a derail guard. The wheel is mounted for rotation about an axis defined by the wheel axle. The wheel has an annular flange on one side thereof, which is adjacent one side of the rail. The derail guard includes a connecting portion, mounted for pivotal movement about the axis of the wheel axle, and a guard portion, depending and hanging pendulously from the connecting portion. The guard portion is disposed on a side of the rail opposite the one side and extends downwardly under the force of gravity. The guard portion is pivotally movable in a direction generally parallel to the rail when contacted by an obstacle adjacent the opposite side of the rail.