The problem is in the model ...
You have left the center of geometry (and hence the center of rotation) of the wheels unchanged and coincident with the geometry center of the model in general.
Every single object that is to be imported as "bone", and therefore can be animated, must have a "ITS OWN" rotation center that will reference any rotation or movement command of the object.
You have to set the geometry center of each wheel in its real physical center.
Another thing ...
I have the habit of choosing a mesh as the main object of the model and parented to it all the other parts.
Using the "DAE" importer, if I did not use this tactic, I found separate objdef, pkg, and mtl files for each model object.
As I see, with FBX importer, this problem should not exist but the habit of creating a "cascade tree" becomes important when the bones of the model become so many.
The movement of each of them will not be independent but will also drag all the bones related to it.
The "strict: true" mode does not allow the use of "constant" in the script. The model suspended in the air does not have any particular powers or properties ... it is simply the sudden interruption of the command code execution that blocks the simulation before the model can touch the ground.
