The Sid rear shock has a positive and and negative air spring. The valves are the two silver knob looking things. The “knobs” are actually the caps. The downside to that shock is that you need a special adapter to allow you shock pump attach to the shock. It’s a small piece. Without it you cant pump up your shock. If you have this piece I’d pump up the positive spring (the top valve) to the desired pressure. The negative air spring is supposed to get the stiction out of the shock. More negative pressure the more supple the beginning of the travel will be. I suppose by having hardly any air in the negative spring it’s like a poor mans platform setting to counter pedal bob.