According to an illustrative example of the invention, a suspension strut of a motor vehicle comprises a protective bellows for the piston rod. This protective bellows protects the piston rod in all positions of the piston rod between an axially innermost operational position and an axially outermost operational position. When the piston rod approaches its axially outermost operational position, the folding bellows is elongated. When the piston rod approaches its axially innermost position, substantially no compression of the folding bellows occurs.