Hi 80robs,

welcome to OSM and thanks for your note.
hw=unclassified and hw=track can't differentiated by road width, surface or smoothness in OSM.
The main difference is the usage. Is it used for traffic between villages or hamlets and access is public it is hw=unclassified.
Is it restricted and only allowed for agricultural and forestal motor vehicles it is hw=track. In Germany it is marked with signs like this[1].
In this case the road connects Dudel and Sandschäferei and is hw=unclassified.

If you have pictures to dermine smoothness=* you can upload them to mapillary.

Regards,
Moritz

[1]: https://wtf.roflcopter.fr/pics/yGW8MDQT/cxQAQcHT.jpg