Old St Albans Road
Took my road bike on this way on 29 January 2023 (following a Komoot route for "bike touring").  Had to walk for some parts, and one slope was very steep (downwards, moving north).
The path was really only suitable for a mountain bike.
Using the OSM surface tags, I'd say the surface is dirt, earth and some large pebblestones.
At this time of year (winter), much of the surface was actually mud.