Ok, this is "the right" way to set FFB.

Centering Spring should be at 100.
Overall, Spring and Damper should be at the same number.

My settings are 139/139/139/100, "Allow game..." unchecked, in-game
40.0/100. I am not very strong person, so I presume that normal male people
should have it at 140%.
I still have some "play" in FFB, but I presume that adjusting
"cockpitLookDeadZone" in app.ini file of iRacing will correct this.

Mario