That looks perfect for an expert mountain biker. mtb_scale=* is appropriate. mtb_scale is not only for formal trails but informal ones as well. You might want to also add informal=yes, although I am not sure it will impact routing.
bicycle=no doesn’t always require signage: as long as it’s actually forbidden (and not just impractical) to ride a bike there, you can map it.
Smoothness also doesn’t imply that there used to be a road, it’s perfectly fine to use on narrow paths (with roller blades, racing bikes, scooters, dirt bikes, mountain bikes, … in mind).
IF it is outright IMPOSSIBLE to ride the path, I think bicycle= no is justified.
If it can be done, then it’s (if we agree on the default) bicycle=yes, and physical characteristics/scale tags should be used to indicate limitations, required skills, etc.
Or use highway=footway, which defaults to bicycle=no.
At the risk of sounding like a very broken record, bicycle is an access tag. I can think of plenty of places were cycling is legally allowed (but not very practical) - many public bridleways in England and Wales for example - and bicycle=no is not appropriate there.
while I agree, there are definitely ways where cycling is physically impossible (e.g. narrow passage between buildings where width is not suffient for bicycle width with handlebars or pedals).
E.g.
A small child on a unicycle would have no problem with that
More seriously, clearly some sort of width tag (and maybe steps) is appropriate there. Here are some more steps with an “official legal right of way on a bicycle”.
A small child on a unicycle would have no problem with that
While I would question it (usually they are not stable enough), assuming for a moment it were true, these aren’t considered vehicles in my countries (but playing equipment).
There is a sport called mountain unicycling (muni)[0] where adults (and some younger folks) ride unicycles over terrain usually ridden by mountain bikers. The vehicles they ride are no more “playing equipment” than mountain bikes. Those steps are probably ridable by someone proficient in the sport.
proficient in the sport, and slim in stature. Frankly, I do not think you can ride a bike on these steps, but I can imagine some artist with good elbow and thigh protection could do it nonetheless. There are also prolific bikers who ride on top of fences, but it doesn’t mean we should tag the fences a cyclable. https://www.youtube.com/@Danny_MacAskill
I’ve seen many discussions about bicycles and the bicycle tag being the legal definition. I think we need a practical sub-tag also.
With people suggesting unicycles are a thing then maybe we need to think of trycyles also; not forgetting wheelchairs.
So that leads me to think of
bicycle:legal= (yes/no)
bicycle:practical=(scale of some sort)
bicycle:note=(descritive note of severe problem)
etc for unicycle, tricycle, wheelchair
yes we have - and it is inadequate which is why this discussion is occurring. I’m suggesting that the tag system be expanded to allow a better description of the wheel ability of the tagging.
bicycle (yes/no) can still exist and greater clarity will be available for a greater description
We do have mtb:scale, but I guess you’re asking for something “below mtb:scale=0”? For those I’d suggest existing tags such as surface, smoothness, tracktype etc. That might still leave a gap for some sort of scale, but please do use already in use tags first.