How can I fix Wheel Colliders Unity5?!

i have so many problem with wheel colliders in Unity 5 pro! 1: the colliders are so big! why they are not match with wheels? 2: when i play my game, the car is jumping up and start spinning, then it fall down and dont stay on terrain! the car just spinning on space!! please help me, what i have to do to fix this huge problem?!!

to big idk but all the other problems is make sure the main parent is rigid and you have a collider like a box the wheels are on they’er own object. and that should work.