Railworks America

Designed a flatcar. Seems fine on the rails till the engine/engine with other cars approaches to couple. Then the flatcar starts to rock back and fourth. It does couple/uncouple from both ends. It can be pulled, but in no time it derails because the car is rocking back and fourth so bad it tilts over. Front and back pivot X appear ok. Collision center y calculated correctly. Collision length is fine. Collision height I'm not sure about. It was calculated with it's load and will never run empty. Maybe recalculate without the height of the load included? (if that's the case then Collision center y is wrong as well). The car mass is 68.1. Maybe too light or heavy? The bogie is 6 axle. First time I've made one so blueprint may have been done wrong. Bogie info for the main blueprint is correct.

Some feed back as to what causes the car to rock back and fourth when a engine or car is near it would be deeply apricated. Thanks.

Found the problem. The bogie was skewed. The left frame was lower than the right frame which in turn showed the wheels on the right were slightly in the air. It was only skewed.0.0012 m but it was enough to mess it up. So that is fixed. Just need to blueprint the car again and then it should work.