IMO, Jack's FFB Tweak files kill a majority of the real driving effects by highlighting useless effects. In a given range, just like sound, only so much is going to fit. You have to make a compromise and focus on which behavior you want to dominate.
Here's some info on the per car tweakers:
- Fx scale (longitudinal forces) - Unless you use really much of this, you will mainly notice this as an added "noise" on the FFB when you hit kerbs etc. Higher amounts of Fx will make the steering wheel counter steer automatically against the slide, but will also make the steering movement on normal cornering feel heavier.
- Fy scale (lateral forces) - You feel this mainly as a force that acts against your steering movement. Very easy to use too much and over saturate the feel making the FFB feel dull.
- Fz scale (vertical forces) - Easiest to notice as a force that turns the wheel in the direction of the turning. Kind of acts as a "counter force" against Fy, so sometimes when you have too much Fy, adding a bit more of Fz can make the wheel feel lighter again while turning (a risk of saturating the FFB signal though if you just keep adding these on top of each others to compensate).
- Mz scale (twisting forces) - Allows you to feel "grip level". Loosing grip will untwist the tires rubber, so adjusting this as high as is possible without creating the "center step" will help you feel better what the car is doing.
- As a general note for all of the above (Mz, Fx, Fy, Fz), when you start to feel a distinctive FFB step/notch near the center of the wheel, you have too much of something there (or too much of all of them ). Or then you might have just a "dull feel" -> then start to go lower starting with Fy.
Also, their is the SoP (Seat of the Pants) adjustment as well which provides some of the non-steering rack forces. Just be cautious as too much of anything will drown something else out.