A variable diameter/width wheel for a vehicle is provided that has an axis of rotation and comprising: a rim, a hub configured for attachment to an axle or shaft, the hub comprising a first part (20) and a second part (22) that are both arranged on the said rotational axis, and arching members (7) having first and second ends and being connected at the first end to the first hub part and at the second end to the second hub part, so that the arching members extend outwardly in an arc between the first and second hub members and form or support the wheel rim, The first and second hub parts (20, 22) can be moved towards or away from each other to change the shape of the arc of the arching members (7) and the two hub parts are lockable in a fixed position relative to each other to maintain a given arc shape. Moving the hub parts (20, 22) towards each other makes the arc shape of the arching members taller and thinner, thereby increasing the diameter of the wheel and decreasing its width while moving the hub parts (20, 22) away from each other makes the arc shape shorter and wider, thereby decreasing the diameter of the wheel and increasing its width.