Cycles In Motion 650b Randonneur

I don't think it's arbitrary, although obviously you're right in that it's difficult to know what 24psi feels like when you're not sure of the starting point.

If you've got a bicycle with set values for tyres width, pressure etc, then replacing the seatpost will feel like you have reduced the psi by (for example) 24psi. We just don't know what the starting values are. I would presume some kind of industry standard like 25c tyre, 100psi or something. Regardless, it's an interesting study. I'm trying to get hold of Josh from Silca's email to bother him about the data.