After the struts are mounted and fully compressed, nitrogen is added to the bottom chamber first. ORI recommends starting with 90 psi the first time around. High pressure in the bottom chamber will resist piston movement and make for a stiffer ride but will be more stable. A lower bottom chamber pressure allows the piston to drop out more easily, and provide a softer ride but will be less stable. The upper chamber must be empty and the strut at full compression when adding or removing pressure in the bottom chamber for an accurate fill. The pressure in the bottom chamber rises significantly as the strut extends.