Ok, coming from the dirt bike world where those pressure release valves are common. It has nothing to do with elevation or temperature change. It's because, even in an air fork, air can and sometimes does pass the seals creating a pressure zone that needs to be evacuated. This is what the those valves are for. I can't believe nobody else has commented on this. Besides that, nice review. I'm getting the 38's 170's for my Trek Rail-7... Looking forward to it. PS I KNOW, i won't be pushing these as far as they can be pushed but I'm look forward to them all the same all the same.