Car permeates through the terrain

Hello!

I hope you guys will help me. I’ve got problem with my car prefab.
When my car is upside down, on the roof, permeates through the terrain.

How I create terrain:
-Create teerain,

  • I raised the value of terrain to 50,
  • Brush-painting area giving the required shape
  • Fixes by mesh smoothing (improved UV maps)
    -Put textures on area,
    -Adding Material that changes the physics of the land
    -Adding Player (our car) to the scene and give it life
    -Appearing the problem then when car rolls onto the roof (the car has colider)
    -Attepmt repair this mistake by giving all sorts of colliders (Box, mesh, several boxes)
    -None effect.
    -Car Done on another terrain works correctly.

Any ideas?
I send you also screenshots:
57247-zrzut-ekranu-2015-10-30-074836.png
57249-zrzut-ekranu-2015-10-30-074839.png

Could it be that you’ve used a terrain imported from Unity 4.x? I have a bug filed where raycasts were inaccurate when a Unity 4.x terrain is imported into Unity 5.x.