Stumbled on a small group of tracks in Italy that were classed with tracktype=grade6 and a surface of dirt. Was this grade ever a thing and might we not want to reclass these to grade5, the barest of the barest in tracks? TagInfo says there are 220 of them
https://taginfo.openstreetmap.org/tags/tracktype=grade6#overview
https://overpass-turbo.eu/s/1ZAo
Sample
Trying to say “4wd only” perhaps? 
Well, grade5 already excludes most all vehicles in routing but agrarian vehicles (tractors) if they would ever use a navigator to go there 
. Certainly bikes are not directed there.
They’re all around the world. I absolutely would NOT use Maproulette for a worldwide challenge like this.
What I would do, on a country by country basis, is find out who added the grade6 tag and ask them what they meant by this tag. It might be a typo, or it might be that they were trying to capture other attributes best stored in other tags. If you ask them, you’ll find out which.
As a sanity check I’d suggest that you visit the ones near you and retag based on your impression of the place.
The ones in Italy are a dozen years old, most have an MTB scale attached to them and are in fact highway=path rather than highway=track. Send a note to the person who tagged those but might not get an answer since only sporadically active.
Wow, turbo response
“No, che io sappia. Ma non sono esperto. L’ho messo ad indicare che non è più praticabile.”
translated as
“No, as far as I know. But I am not an expert. I put it there to indicate that it is no longer feasible”
In other words the smoothness rating kind of impassable. Asked the mapper if that what may serve as a better tag.
Grades 6 to 8 are documented values used in Australia.
Clicked on the wiki tab in TagInfo before and saw a blank page for grade6, a harder find thusly. Now I understand the 4wd comment though. Some farmers here have 4wd Fiat Panda to go around. Already 40 years in the market.
Fact is, if something is found in TI you can count on it going to be used and so it did, in Japan, Europe, USA albeit not much.
