After taking a longer break from VDrift I went back to my old sim code, rewrote it from scratch to be able to run it at full simulation speed.
What I am observing with 360 is that the yaw torque (z-axis) from the front wheels pretty much always (8 - 60 deg slip angle) exceeds the rear wheels. This means the car will always tend to oversteer.
Code:
fz 8982.29 fx 119.966 fy -10776.9 sa -9.128 tz -16293.4
fz 5647.44 fx 146.752 fy -8397.29 sa -9.48577 tz -12997.5
fz 11643.4 fx -515.037 fy -12240 sa -11.3225 tz 13882.3
fz 8464.06 fx -468.251 fy -12412 sa -11.6335 tz 13274.6
...
fz 8398.46 fx 488.18 fy -10090.4 sa -27.2215 tz -15730.1
fz 5128.35 fx 513.325 fy -7386.57 sa -29.8089 tz -11015.8
fz 10880.7 fx 860.208 fy -10601.7 sa -33.3253 tz 10965.9
fz 8122.35 fx 888.05 fy -10530.3 sa -35.9443 tz 12305
What we see here is that the front to rear weight ratio can not offset the front to rear lever ratio. So even when the rear wheels have more grip due to higher load, the front torque is still larger.
I've been wondering why the real car doesn't have this issue. At some point, after going through 360.car params a couple of times, I've noticed the difference. The rear tires are 30% wider, 215 mm vs 275 mm. This is something we don't simulate in any way.
With the pacejka tire model, this means different tire params for the rear wheels, to fix the oversteer tendency. The question here would be, how much does the grip vary with tire width (contact patch size)?
