To make your mountain bike behave predictably, the fork's sag needs to be compatible with the shock's sag.SRAM recommends inflating your shock based on your weight in pounds: one pound is equal to one psi.Multiply your weight (in full kit) in kilogrammes by 2.2 to get your weight in pounds. So if you weigh 73 kg in all your kit, you'll be 160 pounds (73 x 2.2) and will need to set your shock to 160 psi.Click the link below to learn more about adjusting your shock's sag.NB: The valve's cap is there to protect the valve from dust. It doesn't do anything to retain the pressure. So there's no point doing it up too tight!