Directional stability

[NaN]

I've spent some time trying to figure out the reason for unstable car behavior during braking.

My first suspicion has been tire lateral force symmetry. Making sure that the tires are left right symmetric hasn't fixed it though.

Next was the center of mass offset due to driver position. Adding a balance weight still didn't help.

What I've learned though is that the effect is caused by positive feedback of current slip angle. As soon as there is a minimal slip angle it will generate forces that depending on center of mass and weight transfer(braking) will act to increase the slip angle.

Why does it not happen with real cars? From my current understanding the reason is steering caster which allows wheel self centering and gives cars/bikes directional stability, counteracts to slip angle variations. VDrift doesn't simulate this self centering, the wheels are seen as fixed relative to chassis at any time.

How to fix it? I had some success (have got the CO to stay stable during hard braking) by carefully adjusting the toe and camber values of the front and rear wheels. But it also means that with any change to camber, toe or center of mass one has to check the car for directional stability, which is not optimal.

What I haven't found out yet is whether the reason for the initiating slip angle is due to numerical instability or some simulation bug. I can clearly affect the direction by messing with front and rear camber/toe, make it pull to left or right.