If you want to be geeky measure the height of the tyre unloaded from the ground to rim Now when you sit on the bike it should be 9% smaller with the correct pressure for your weight
Source? Is that tyre unloaded as in no reaction force between the tyre and ground?
Would have to be rider only, as it would be impossible to measure any reaction force.
All seems a bit teachy to me, run my tyres at 115psi whatever, commuting or taking part in long distance / chairty ride.