By the way - what's the solution for those big stiffness values? How to make it act like hard surface rather than catapult? I am trying to solve this for tires. Currently my manually coded tire is bouncing up and than falling. And it's very quick. At lower stiffness, however, it falls through floor. How would I manually stabilise it at the same time keeping the property of elasticity and bounciness?

Are you using Physx? If you have an approach like mine I can give you my physics values that work somewhat fine for me (at least on "normal" underground)

(In terms of Stiffness, Damping, BaseForce, Vehicle Weight, Gravity Force and so on)

No... I am using Bullet. However, the matter is different. I have tire with no collisions. I cast ray(as a collider). There will be more rays later. The ray works as a spring. It moves the tire accordingly(force/mass). I also apply damping. However, damping doesn't help. The tires are out of control at high stiffness. It's bouncing up and falling down. It acts crazy. I don't know how to stabilise it without high frequencies. And I don't know how to read Bullet or PhysX source codes.