For a long time I am searching for the correct way to setup FFB, and
finaly I got it. To set things rightly, I first have set my FOV correctly,
the hight of screen correctly, and latency (it turned out that this wasn't
necessary) correctly. I determined the latency very low, at 0.000715 in
iRacing (the default is 0.050000).
So, what is the secret. FFB is actually the play between Spring,
Damper, and the strength of your hand (it looks like). Centering Spring
(unchecked) has to be at the same value as the Overall setting. You leave
the Damper and Spring at 100%. Now, when you rise Overal/Centering Spring
too high, you feel too much damper. Lets say you start with both at 150%.
Then you go lower by 5%, and you will still feel too much damper. Then
suddenly, you start to feel too much spring. This change happens at my rig
between 130% and 125%. At 130% I feel damper, at 125% I feel spring. The
correct setting on my rig (neither damper, nor spring) is 127%, so I have
settings 127/100/100/127.
The VERY good news (actually, excellent news) is that latency
doesn't affect the controlability of such set FFB. In fact, although I
CLEARLY feel *a lot* of latency at iRacing's default latency setting
(cockpitLookDeadZone = 0.050000, in app.ini file), car is actually MORE
controlable with that latency than with low latency (0.000715). With the
default latency going over curbs is real delight, when you overshoot a
corner there are no bigger problems (car behaves like a real car), and in
other tricky situations it is actually BETTER to have the iRacing's default
latency settings (after all, cars also have latency, so what, as long as it
is controlable). My times are still close to my personal bests even with
high latency, although with only few laps driven.
I still didn't try with vsync on (I had enough of testing for
today), but it would be excellent if this works with it, becaue 3D things
use vsync.
I must say that I have pretty well set FOV and hight of screen (I
set it with the precission of 0.005%, so pretty well), so I have no problems
regarding this (which you might have when trying this).

Mario