Best way to add a MeshCollider at runtime without ruining physics?

Hey! I need to add a meshcollider to my vehicle at runtime but as soon as I do it will ruin physics entirely. The car will clip at 20mph, and roll over 4 or 5 times. Not it is not stabilizer bars, yes I am adding them, yes the CoG is correct.

Here is a snippet of the code

         //RIGIDBODY FIRST!
         car.AddComponent<Rigidbody>();
         Rigidbody r = car.GetComponent<Rigidbody>();
         r.interpolation = RigidbodyInterpolation.Interpolate;
         r.collisionDetectionMode = CollisionDetectionMode.Continuous;
         
         car.AddComponent<MeshCollider>();
         MeshCollider CCgb = car.GetComponent<MeshCollider>();
         CCgb.convex = true;
         //CAR COLLISION!
         Mesh carColliderMSH = tmdl_load.LoadTML (CarFile + "/" + CarName + "_COLLISION.tml",true,false).GetComponent<MeshCollider>().sharedMesh;
         CCgb.sharedMesh = carColliderMSH; //This messes it up =c
         //Calc physics?
         car.SetActive (false);
         car.SetActive (true);