HELP! why my vehicle lean towards side or front?

I tried to make a vehicle by my-self and used a model download from the web site. The model was adjusted in Maya.

The physicsAsset is liking this:

After I set the corresponding wheel in “vehicle setup”, and play

The car always lean towards front like this:

I am a newer to unreal engine and working on this problem for several days without any progress. Is there anyone can help me or give some advises?

Thanks a lot!