Tagging road for motorbikes but not for cars

How do I tag a road, which is

  • too small for cars, big enough for motorbike;
  • with concrete surface;
  • important (for locals) since it is part of a market area
  • in an area (Vietnam) where most traffic is made by motorbike.

All the highway or path tags seem not to fit since either they imply that cars can go there or they exclude motorbikes somehow. Maybe there is something to indicate a small width of the road?

You can use http://wiki.openstreetmap.org/wiki/Key:narrow and/or http://wiki.openstreetmap.org/wiki/Key:width on the highway. This won’t limit what type of vehicle can use it, however.
About the restrictions, you can tag like this: access=no + bicycle=yes + foot=yes + motorcycle=yes (it means that it’s only allowed for bicycle, pedestrians and motorcycles). You can play with access (http://wiki.openstreetmap.org/wiki/Access#Land-based_transportation) to see if some other restriction solution better fits your needs.
For the surface, it will be surface=concrete (http://wiki.openstreetmap.org/wiki/Surface)

Thanks! The problem with access is, that it models the law, not the physical access possibility of a road. Thus i think I will use the width-tag.

If it’s too narrow for cars => highway=path

http://wiki.openstreetmap.org/wiki/Tag:highway%3Dpath

I agree with Pieren.
In Indonesia, such ways are called “jalan setapak” (hand-wide roads).
For easy distinction from hiking paths which cannot be used by motorbikes, please add appropriate access tags (it’s rather inconvinient when your navigation unit suggest a route on a hiking path…). A surface tag is also appropriate, as many such paths in south east asia are not paved.

It rest that path is modeling the legal access, not the physical accessibility. It seems to me that there is no convenient way in OSM to roughly indicate a physical accessibility to different kind of vehicles. Only the very detailed width-key, or the actual wrong highway=path tag. Anyway I understand why one could use the path-tag. I think there should be a new key introduced, roughly describing the physical accessibility to different kinds of vehicles.

No, “path” is modeling the physical accessibility and highway importance. Check the wiki. The legal access is determined with the key “access”.

I read the wiki very carefully, maybe I did not understand it very well. The wiki states, that path is

In the whole description you find only one possibility to “tag separately” a different “intention” of the way, i.e. to tag it can be used by motorbikes: This is the access key.

Also, the wiki page states that

So all in all, the whole thing is about legal access, I nowhere find anything about physical accessibility. Please tell me if I missed something!

To me, confusion starts when I consider that path is a value to the highway-key, which indeed aims at modeling the importance of the way. Anyway, the description of path tells me nothing about the importance or usage of the way (like all other common values to highway do).

Use surface, smoothness and width (maybe also maxwidth:physical and maxheight:physical, but this may get esoteric and not useful) then each user can infer if this road is physcial suitable for his vehicle and style of driving.