Mass is how difficult it is to make an object move. The moment of inertia is how difficult it is to make it rotate. If the moment is very low in relation to the mass, then the high mass will create a large impulse and the low moment will make it too easy to rotate. In your case, the low moment is probably several orders of magnitude to low. Instead of a slight correction to the rotation, it creates a *huge* one. This causes the rotation twitch back and forth erratically as the contacts change, almost completely changing from frame to frame.
The moment functions are not too complicated, and can be found here:https://github.com/slembcke/Chipmunk2D/ ... munk.c#L92
If there isn't a wrapper/port for them, it shouldn't be hard to do it yourself.