Eureka, I finaly found the Holy Grail of FFB, : ).
The problem with FFB forces is slack. I found the way to balance
that slack. It's done with the Overall slider. On my system the slider
should be at 138%.
This way everything works as intended. I tried this with different
Spring/Damper/Centering Spring combinations, an it works with all of them,
even with 0/0/0, or with 0/0/100.
Of course, you'll drive car the best if FOV is natural.