Shock absorber for a wheeled vehicle, or for a seat of a vehicle, said shock absorber comprising at least one fluidic damper constrainable between at least one wheel, or the seating of said seat, and the frame of said vehicle and equipped with a cylinder and a piston sliding within said cylinder, and at least one gas spring functionally combined with said at least one fluidic damper and acting for at least part of the stroke of said piston with respect to said cylinder, wherein said cylinder comprises a first chamber and a second chamber and that said piston slides within said cylinder thus varying the dimensions of said first chamber and said second chamber, said fluidic damper further comprising a rod integrally combined with said piston and adapted to make said piston slide inside said cylinder, said rod being equipped with an inner housing in which said at least one gas spring is housed, and said gas spring being functionally combined with said at least one second chamber and/or said at least one first chamber of said cylinder, wherein said at least one gas spring comprises at least one third chamber and at least one fourth chamber, said at least one third chamber containing a gas, wherein said at least one third chamber and said at least one fourth chamber are separated from each other, directly or indirectly, by at least one sliding, or deformable, dividing wall and wherein said at least one fourth chamber is in fluidic communication with said at least second chamber, said at least one fourth chamber and said at least one second chamber containing an incompressible fluid transferable between said at least one second chamber and said at least one fourth chamber, and vice versa, as the position of said piston varies with respect to said cylinder, said at least one dividing wall being, further, sliding, or deformable, depending on the volume of incompressible fluid transferred from said at least one second chamber and said at least one fourth chamber, and vice versa, so as to vary the volume of said third chamber, said housing of said rod comprising said at least one third chamber, said at least one fourth chamber and said dividing wall, and wherein said shock absorber comprises first adjustment means to adjust the pressure of said gas inside said at least one third chamber, said housing comprising a hole obtained within said rod, and said gas spring comprising a fifth chamber and at least one second dividing wall to separate said at least one third chamber from said at least fifth chamber, said second dividing wall being sliding, or deformable, so as to vary the volume of said third chamber and said fifth chamber, said fifth chamber and said second dividing wall being arranged within said hole, characterized in that said first adjustment means further comprise at least one sixth chamber fluidically connected to said fifth chamber, said at least one sixth chamber and said at least one fifth chamber containing an incompressible fluid, said incompressible fluid being transferred by said first adjustment means between said at least one fifth chamber and said sixth chamber, and vice versa, said at least one second dividing wall being further sliding or deformable, depending on the volume of incompressible fluid transferred from said at least one fifth chamber to said at least one sixth chamber, and vice versa, and in that said gas spring also comprises a further chamber arranged between said third chamber and said fourth chamber and at least one further dividing wall to separate said further chamber from said fourth chamber, said gas spring also comprising at least one elastic spring having a first end resting on said first dividing wall and a second end resting on said further dividing wall.