Spoiler for motor vehicle provided with a passive mobile element

The invention relates to a rear spoiler for a motor vehicle, intended for being arranged in a region of a rear edge of the roof above a rear window, said spoiler including a first portion provided with an upper surface substantially aligned with an imaginary extension of an air-flow line of the roof. The spoiler is characterised in that it includes a second portion, mounted movable relative to the first portion, between a retracted position (upstream) and an extended position (downstream), in which the spoiler portion projecting above the rear window is increased, and a passive movement system capable of moving the second portion as a function of the air flow on the upper surface of the spoiler.