How can I set my wheelcolliders the the Car does'nt roll if it stands on uneven surfaces? I tried to increase the stiffness factors extremely but it doesnt work.
If you mean the sliding of a stationary car down a slope then the answer is you wont stop it using the tyre model provided by the WheelCollider system, you will need to write your own tyre model to replace the forces or do a raycast system with your own tyre model. Its a limitation of the force combiner in the PhysX tyre model, it relies on some slip angle or ratio to generate a force and at very low speeds or zero speeds the system gives a zero force so allowing the car to slide a little due to gravity this small movement then makes the tyre model generate a force again which stops the movement and so on.