A slider bar for use with two-door style motor vehicles for anchoring the lap belt for front seat occupants. The slider bar allows the lower anchorage point of the lap belt to freely move in the fore and aft direction to enhance rear seat compartment passenger ingress and egress. The slider bar further incorporates a pyrotechnic lap pretensioner (PLP) function for exerting pretensioning motion of the lap belt in response to a vehicle impact. The slider bar incorporates an internal piston which acts on the belt webbing position on the outside of the slider bar tube. Various embodiments are described incorporating alternate means of mounting the lap belt lower end to the slider bar, as well as various configurations for transferring the motion of the internal piston to the lap belt lower anchorage.