And I have also to admit that because its often extremely difficult to correlate a theoretical correct change in as example the power/coast settings
with the resulting outcome in car behaviour - so my personal conclusion have been: why the hell make it even more complicated (using 3x different diffs ) when the sim devs cannot even make the clutched diff to function correct.
Depends on physics engine: madness has the whole drivetrain simulation very detailed, with components also flexing, cogging and in general "not being ideal", so they're exposing the settings you'd have on a real race car while other sims are letting you set only the effects of those changes. Just read the post i linked from pcars2 forums for a very good explanation.
CatsAreTheWorstDogs: This postulate is not a personal vendetta against the diff devs - but something I have concluded after reading peoples advices about as example how you should set up the coast in rF2 or iRacing to get the corner entrance more oversteering(rotating).
Because I have forund advices saying the complete opposite of each other.
I think this has much to do with the fact that differential settings shouldn't be tried by doing too large changes: what clutch diffs do is mainly use torque from the engine to couple wheels and force them to have the same rotational speed. The more torque the car has, the more lock you get with same diff settings, the more grip your tires/aero gives you, the more locking you need to actually force same speed during a turn (you have to overcome inside wheel's grip to force it go same speed as outside one).
Basically coast forces you to go straight qhen you use engine braking, if you have "large" grip differences betweeen rear tires (cambered brake zone, rough surface, lateral load on suspensions) more locking helps making the car stable, but if you don't actually have issues in any brake zone increasing coast lock could lead to instability: it could be that you were alternatively micro-locking rear right/left tires, if you lock them, you may end up making them both slide together getting an "handbrake" effect with the car spinning.
With preload you're forcing your internal tire to go faster and external to go slower mid-turn, this makes the car more stable UNLESS you actually want to steer more than that "stabilizing force" allows you to, at that point one or both tires have to "give up".
You can see the effects of a 100% locked diff (equivalent to infinite preload) on the SC V8 or on the karts: mid corner they either understeer as hell, drift or lift the inside wheel.
Power also similar to the others, but this time the engine plays a major role: an open diff will tend to just spin the inside wheel if you use too much throttle on corner exit, making you just waste power with no traction, but still having full lateral grip on outside wheel.
This behaviour will create understeer BUT the fact that it is not locked will still make the car more "agile" (and oversteery) if you're NOT spinning the inside wheel. It also is less predictable when going back to grip. A locked one, as always, lets the car rotate less and have better traction UNLESS you actually want to oversteer: as i said open differential doesn't let you spin easily, a locked differential understeers untill BOTH wheels start to slip, making you oversteer and even have a nice drift on exit while still being predictable.
SO when setting up differentials you shouldn't just try extremes, because they are actually something you won't want to race with, just finde the values working with your driving style (i brake late and like it understeery on brakes but agile off throttle -> mid coast low preload, but this makes the car unstable mid-corner, high power lock lets me balance this with throttle: when i accelerate i get lock and the car stabilizes, but i can also use even more throttle to start a little slide and rotate it)
WHEN I SAY LOW/HIGH I ALWAYS TALK ABOUT LOCKING, NOT VALUES YOU PUT IN SETUP, IN AMS/PCARS2 HIGH LOCK = LOW ANGLE AND VICEVERSA
Lower the downforce (wings) to a degree where you are still able to control the car but where you are closer to tiptoeing the car round the track more than you feel comforting with.
Because now its a lot easier to feel what effect a change in power/coast settings does initiate.
While this is valid if you want to get an understanding of what that setting does, when you put downforce again on the car you'll most likely want to change diff settings too.