A wheelchair (1, 1'), comprising: at least one modular power chair base comprising at least one connection point on each side of the modular power chair base for connecting at least one modular wheel assembly (3, 3') to each side of the modular power chair base; and at least two modular wheel assemblies, each comprising: a frame member (7, 7'), at least one castor wheel (9, 9') attached to the frame member (7, 7'), at least one drive wheel (11, 11') attached to the frame member (7, 7'), and at least one castor arm (13, 13') adapted to carry the castor wheel (9, 9'), wherein • the frame member (7, 7') comprises at least one first connection member for connecting the modular wheel assembly (3, 3') to a connection point on the modular power chair base of the wheelchair (1, 1'), • in a first configuration, the drive wheel (11, 11') is arranged offset to a first side of the frame member (7, 7') out of alignment of a centerline of the frame member (7, 7'), • in a second configuration, the drive wheel (11, 11') is arranged offset to the second side of the frame member (7, 7') out of alignment of the centerline of the frame member (7, 7'), and • the second side is opposite to the first side, wherein one modular wheel assembly (3, 3') is connected to each side of the modular power chair base, and the two modular wheel assemblies comprise one modular wheel assembly (3, 3') of the first configuration, and one modular wheel assembly (3, 3') of the second configuration, and the wheelchair (1, 1') is adapted to be converted between the front wheel drive mode configuration and the rear wheel drive mode configuration by swapping the two modular wheel assemblies on the sides of the modular power chair base. at least one modular power chair base comprising at least one connection point on each side of the modular power chair base for connecting at least one modular wheel assembly (3, 3') to each side of the modular power chair base; and at least two modular wheel assemblies, each comprising: a frame member (7, 7'), at least one castor wheel (9, 9') attached to the frame member (7, 7'), at least one drive wheel (11, 11') attached to the frame member (7, 7'), and at least one castor arm (13, 13') adapted to carry the castor wheel (9, 9'), wherein • the frame member (7, 7') comprises at least one first connection member for connecting the modular wheel assembly (3, 3') to a connection point on the modular power chair base of the wheelchair (1, 1'), • in a first configuration, the drive wheel (11, 11') is arranged offset to a first side of the frame member (7, 7') out of alignment of a centerline of the frame member (7, 7'), • in a second configuration, the drive wheel (11, 11') is arranged offset to the second side of the frame member (7, 7') out of alignment of the centerline of the frame member (7, 7'), and • the second side is opposite to the first side, a frame member (7, 7'), at least one castor wheel (9, 9') attached to the frame member (7, 7'), at least one drive wheel (11, 11') attached to the frame member (7, 7'), and at least one castor arm (13, 13') adapted to carry the castor wheel (9, 9'), wherein • the frame member (7, 7') comprises at least one first connection member for connecting the modular wheel assembly (3, 3') to a connection point on the modular power chair base of the wheelchair (1, 1'), • in a first configuration, the drive wheel (11, 11') is arranged offset to a first side of the frame member (7, 7') out of alignment of a centerline of the frame member (7, 7'), • in a second configuration, the drive wheel (11, 11') is arranged offset to the second side of the frame member (7, 7') out of alignment of the centerline of the frame member (7, 7'), and • the second side is opposite to the first side, • the frame member (7, 7') comprises at least one first connection member for connecting the modular wheel assembly (3, 3') to a connection point on the modular power chair base of the wheelchair (1, 1'), • in a first configuration, the drive wheel (11, 11') is arranged offset to a first side of the frame member (7, 7') out of alignment of a centerline of the frame member (7, 7'), • in a second configuration, the drive wheel (11, 11') is arranged offset to the second side of the frame member (7, 7') out of alignment of the centerline of the frame member (7, 7'), and • the second side is opposite to the first side, wherein one modular wheel assembly (3, 3') is connected to each side of the modular power chair base, and the two modular wheel assemblies comprise one modular wheel assembly (3, 3') of the first configuration, and one modular wheel assembly (3, 3') of the second configuration, and the wheelchair (1, 1') is adapted to be converted between the front wheel drive mode configuration and the rear wheel drive mode configuration by swapping the two modular wheel assemblies on the sides of the modular power chair base.