I haven’t started mapping single-track motorcycle paths/tracks yet because I see some problems with the tagging.
Option 1
Guidance on NPS trails says make them highway=track, motorcycle=yes
https://wiki.openstreetmap.org/wiki/US_National_Park_Service_Tagging:_Trails
Option 2
This wiki says highway=track, atv=yes because “atv=yes” implies motorcycle and restricts width to less than 50".
https://wiki.openstreetmap.org/wiki/Key:atv
Option 3
There’s a third possible combination with highway=path and motor_vehicle=yes or maybe motorcycle=yes.
https://wiki.openstreetmap.org/wiki/Tag:highway%3Dpath
Problem with both options 1 and 2 is that its still rendered as a track and there is no style change to indicate there would be a width challenge for a automobile. The data is there to prevent routing by the routing engine, but no visual queues in the rendering to tell me I’d get stuck in a jeep.
Option 3 fixes the understanding of width in a rendered map, but unfortunately the default access is no motor vehicles and, there is no visual queue to tell otherwise.
Why on earth don’t we have something smaller than a track that can be used for motorized vehicles (ATV, Motorcycles, Electric Bicycles)?