Abstract: A method of assessing the stability of a wheeled mobility assistance vehicle 1, by determining the position of the centre of gravity of the vehicle. There are arrays load sensors (8, 9, 10, 11) on which the wheels (3, 5) of the vehicle are placed, the sensor arrays providing data sufficient to permit determination of the position of a wheel. The sensor arrays supplying data to data processing means (13) which calculates from that data the load imposed by individual wheels of the vehicle, the positions of those individual wheels and thus distances between the wheels of the vehicle. The distances between wheels and the loads imposed by the heels of the vehicle are used to determine the position of the centre of gravity of the vehicle.