There is definitely something going on regards adjustments in tyre pressure.
The way it affects the tyre and subsequently what vibes are felt is real.
I've been playing with the pressures and went up as far as 43psi (circa 3.0 bar)
The vibes were worse than they have ever been before!
Think
@seamust1000 cattle grid example.
Back down to 41psi. Imperceptible!
I know the circumference should not change much, (if at all) but the amount of tread in direct contact with the road might?
Again, I can't see how or why, but just know that it does.
I've been reading up a lot on the 'tinternet' and there seem to be many arguments both for and against how different a tyre can be at different pressures.
Extremes of pressure, I can understand, 10 psi for example.
I mean, some modern TPMS are triggered when a tyre deflates, thus altering the circumference to a degree that the computer can see, via the ABS sensor, and trigger the alarm. (Happy to be corrected by
@siteguru OBV's.)
The tyre then, I presume? can be taller or shorter (if you catch my drift) thus changing various angles in the related drive shaft to motor connection?
This must be having an effect on what we feel at the wheel or in the seat?
Sadly I don't have the definitive answer, but I just know it makes a difference.
To be clear, it makes a very real difference to me.
So much so, that if my car had been running at 41psi from new, I don't think I would have noticed a thing.