car with wheel collider fall thought road collider

Hi, i created a car with wheel colliders, on flat primitive cube collider it rides very well, but when i create some more difficult road collider with several polygons and uneven surface, in some edges (not every) between 2 polygons my wheels fall through the ground, bottom of the car falls on the ground and car can’t ride more… i can’t understand how must be created road collider… i tried to create flat and volumetric mesh collider, with many variations of polygons and polygon sizes… and in every case cars find some plase in road where falls … only primitive cube collider works true, but i have big city with many difficult roads, and primitive colliders don’t help me…

p.s. sorry for my terrible english)) it’s not my main language…

nobody can’t help me?(