Center of gravity changes according to sliding seat. (For safety reasons, center gravity of end-user will always stay above the middle wheels) Mechanical shear reduction device for injury prevention. Armrest adjusted automatically when reclined for comfortable seating. Adjustable seat width and seat depth (16"/18"/20") for customerized fitting of individual user. Removable battery case for replacing and maintaining battery easily. Dual in-line motors for enhanced efficiency, torque, range and performance. Full front and rear suspension design offers a comfortable ride. Power tilt operated in 5?~55? for pressure relief. Power recline adjustment from 90?~150?. Optional seat elevator and power footplate or elevating legrest. Optional PG R-NET multi-function controller.