Other great tuners may offer their expertise.
My simple (I’m not tuner) explainatiins that have got me through when I can find a shared tune that I like it was in a spec race and need to change for track.
More then likely your using the default ARB setting and this is how I go with them.
Front ARB all left and rear ARB all the way right is max oversteer and opposite is min. For ARB setting
I treat suspensions with the following.
If I feel I need more front end grip I will move slider to left on front.
If I feel rear needs more grip I will move the rear slider left. I usually will start in 100 to 200 lb increments then narrow it Dow to 50 then 25. When I like balance. I keep the relationship between front and rear and try stiffer as whole and softer as whole to see how I prefer the car.
Chamber for depends on track but I will listen to tire squeal. I tend to start at -2.0 and -1.5 and I adjust. This does help on certain turns as the car rolls in a turn the outside ends up getting more contact patch and more grip. Drag racing and straights probably should be zero. (Project cars to get better straight line speed reducing chamber was the ticket)
Toe if I’m racing I tend to want predictability and I find a bit of negative toe on rear helps car follow the fronts. Put positive toe can help the car turn in better. However I like to leave this to last and higher speeds prefer 0/0. (My opinion. Everyone is intitled to their own.)
So if after adjust acel/decel, ARB, springs and rebound I still want more I start adding positive toe to front.
Accel/decel diff are my favorite change to run car in stock form and adjust drivability. (Fm5, 6 seemed to have wickedly low decel difs so I be grown accustomed to them)
Accel dif I use for the amount of power I put down and lessen tire spin and help throttle oversteer. Move slider to right more throttle oversteer to the left if you can not manage it. I’ve had vettes that just smoked tires no matter what I did and lowered the accel dif and it was drivable
Decel diff. I like to have this as low as I can stand. When you come off throttle the lower the setting the more oversteer/ rotation you will get. Especially helpful for the setting up a turn. Lift/brake and car and rear will start coming out and your be able to take turns tighter. Raise it to lessen the effect, lower to gain more.
Rebound. (I swear sometimes there is no rhyme or reason in the game setting for this) but I tend to treat similar to ARBs the further left fronts relation. To rear the more oversteer while the car is accelerating or deceleration. (I.e. Not neutral) I tended to do ARBS in coasting turns. And rebound in accelerating out of turns.
But I’ve seen rebounds set to 1 and bump set to 13. So god only knows what it does or doesn’t do.
If I was you I would make no correlation of game to real life. It’s a game and it’s ruled by its physics model not real life.
If I had car that understeered I would like and wanted quick fix I would move front ARB left, maybe move rear right depends on where it is. I would check the decel diff. Make sure they are low. In AWD I have zero on Front and can get close to zero or be zero on the rear. Then start adjusting to your suiting. You’ll see the car will start to become better.
Some cars are just better then others. Rockets. Don’t like to turn and some grip monster run on rail cars don’t like to be rockets on straights. You can make some cars better. But their nature is still there