To be honest i'm a relatively new programmer and I know the basics of wheel colliders. For some reason I can not make a stable or good car. This is probably a bad request but I would like someone to put an example of a wheel collider. Just the wheel collider stats, the rigidbody stats, (because the two are linked) and the distance between the wheels. I will not directly take your wheel colliders, I just need a working example to experiment with and change. It is just a lot easier to know what works and what does not when you have a working example.
Have you tried taking a look at the Standard Assets vehicle physics? https://www.assetstore.unity3d.com/en/#!/content/32351
Maybe you can check this too: https://www.assetstore.unity3d.com/en/#!/content/83660 Anyway, dont worry, you are not alone: https://forum.unity3d.com/threads/unity-5-wheelcollider-component-is-unusable.307099/
I have been struggling with this myself the last few days due to lack of description on what the functions on the wheel collider actually do until I found this beaut https://stackoverflow.com/documentation/unity3d/4405/collision#t=201708032354445041154 Hopefully it makes a lot more sense, Unity should include these explanations in the wheel colliders code comments / descriptions.
Not only wheel colliders code comments / descriptions, and some Examples codes snipes, to get started. In my opinion