Hi Jon,
I was originally attempting to indicate lanes, paths and quiet roads (eg. modal filtered) which can safely be used for utility cycling and represent local permeability.  This includes some moderately loose surface paths which I often find more comfortable to use than tree-root and pothole riddled cycle paths (on 28mm tyres), but definitely not mountain-bike-only style trails.  Network class = lcn seemed to be the closest fit for this requirement, based on usage elsewhere, but I'm happy to update this if there is a better way of representing a tried-and-tested community network.
The ultimate aim is to improve accuracy of route planning using cyclestreets.net, btw.
- K.