Finally managed to sneak up on my problem, and get a log without rF2 blowing up. Suspension isn't the issue. The tire rotation speed just goes bananas, for no apparent reason. (at over about 220km/h) I've redone the lookup tables for the M_30-65-18x11.5_S9M_Slick_2017.tgm to much higher speeds, and reduced calcpointaccel to 0.4, to make ttool capable of the higher speeds. (model had this problem earlier already though) So, to my actual point, does anyone have a idea of what parameter to adjust to stabalize the numeric solution for the rotation speed?

This problem will be caused by an instability resulting from the stiffness frequency of the ring (tyre carcass) and rim interaction reaching some threshold. Even though we're running at 2400Hz, the point it can become unstable is as low as 200Hz. There are 2 (main) ways to curtail this, that is, to reduce the ring stiffness in pitch, you can do this with a simple multiplier. That is reducing the 4th parameter, here RingStiffnessMultiplier=(). You could do that by using a higher angle for the carcass plies, but that's generally going overkill. The 2nd method is increasing the inertia of the complete wheel, which might be the way to go if there's a chance you underestimated that..

Huge help Michael! I modified RingStiffnessMultiplier=(1, 1, 1, 0.9, 1, 1) to RingStiffnessMultiplier=(1, 1, 1, 0.75, 1, 1), works great now! I tried 0.6 first, which also worked, but would heat up the tires at a crazy rate at high speed with some camber. (and also switched to the M_31-71... slicks) Out of curiosity, is it possible to modify the rim "pitch" stiffness separately from it's radial and axial stiffness?