interesting the R is 29/29 I guess the Z is heavier and different weight balance.

My curiosity is the reason for using a different pressures to the handbook (within a certain parameters: normal road use/ standard tyres/ no extra weight) not extreme use.

I found that with my recent tyre change to a different manufacturer, I now run the rear at 26~27 to calm the bumpy rear end.

BTW 2psi difference from standard is noticeable in terms of handling and bump absorption (perhaps even 1 depending on how much natural padding you carry)