Complex sentence: It is based heavily upon the Aprilia RSV Mille and its successor, the Aprilia RSV1000R superbike with which is shares its engine, gearbox, frame and, partly, its suspension.
Split into simpler sentences: It is based heavily upon the Aprilia RSV Mille. Its successor, the Aprilia RSV1000R superbike shares its engine, gearbox, frame and, partly, its suspension.