An improved lower anchor strap tension adjusting mechanism for varying tension in a restraint connected to a vehicle. The mechanism comprises first and second adjuster ends and a length of web spanning therebetween. One end of the web is attached to one of the adjuster ends. A guide is provided on one or both adjuster ends enabling the web to be looped around the guide(s) and between the ends in multiple passes. A web lock device is connected one of the ends to engage the web and allow the length of the web spanning between the first and second adjuster portions to be fixed. The number of loops of web spanning between the adjuster ends determines the mechanical advantage in the tension force applied to the anchor strap by the adjuster compared to the tension applied to the free end, improving ease and security of safety seat installation.