Andre, I'm sure can give more detailed response than my own but thought I'd try to help understand ...
The log window will give you an idea...
Eg:
Porsche 911 RSR GT3 (Assetto Corsa)
Effect 7 (Engine Beat 2)
You can also look at the Asus EQ activity
With this car it is not active above Start Effect @10%
This determines when its active within the cars RPM range
This car's range (900-9000 RPM)
At idle is 900 RPM, so below 10% will be below idle RPM value, therefore, active @ 9%.
The more you have the Gain slider set the more the AD gain will be (see log)
Porsche 962
Log data:
Idle 1900 RPM Max 8400 RPM
So this car needs to be below "Start Effect 23%" to be under the 1900 RPM value.
Different cars may also generate different AD gain values based on the gain slider position.
One car at 50% slider value may not feel the same as another.
My Personal Opinion:
This is just one reason why "saved presets" using custom wav should not be automatically overwritten by casual adjustments. Additionally, loads of people will perhaps use one profile set of custom .wav with various cars but again casually just move the sliders or in this example the "Start Effect %" needing to be altered.
The "Additional Tone %" is another example, on the Porsche 911 RSR GT3 its perfect at 95% but different cars will need different values to have the tone kick in at the optimal RPM or rev counter lights.
The crash element could be "Wheel Slip" and if its set at a low value you can see in the log its active when in idle. Crank it to 100% Gain and you will see it active in the Asus EQ.
Various factors here, could depend on the .wav used, the Gain % and different cars if or how much this may be felt.
Wheel Slip will activate with collisions. You will find several effects do but oddly "Damage" will not.
I have had instances when I hit escape to pause AC and "Wheelslip" remains active.
Im sure others have encountered this as well.
Hope its some help....