It is coupled with a two-stage gear-drive that increases torque by a factor of 13, without which the motor would not be able to move the vehicle when a person is on board. However, the motor is vulnerable to overheating. The torque increases as the load on the vehicle increases, for instance by going up too steep a gradient.[6] Sinclair's tests showed that it could cope under power with a maximum slope of 1 in 12 (8%) and could manage a 1 in 7 (14%) slope using the pedals.[8] As the speed of the motor reduces, the current flow through its windings increases, drawing up to 140 amps at stall speed.