An update, to fix some errors and take into account the @ftrebien’s comments:
| Feature | grade1 | grade2 | grade3 | grade4 | grade5 |
|---|---|---|---|---|---|
surface(1) |
Any paved surface | gravel, compacted or fine_gravel |
Any unpaved surface | dirt, sand, grass and the like |
grade4 surfaces or mud |
smoothness by definition(2) |
bad or better |
intermediate to bad |
intermediate to bad |
intermediate to very_bad |
intermediate or worst |
smoothness in practice |
good or excellent |
Same values | Often also tagged very_bad |
bad or very_bad |
very_bad or horrible |
*:visibility |
excellent |
excellent |
excellent |
excellent |
Any |
| Drainage Systems | Possible | Possible | Seldom | Seldom | No |
| Added Materials | 100% | > 50% | Up to 50% if necessary | Only where necessary | No(3) |
| Max. Incline | Common inclines | Usually < 15%. Steepest sections are paved. | Usually < 15%. Steepest sections are sometimes paved. | Up to 15% | Any |
| Puddles(4) | Shallow | Shallow | Shallow | Deep and half track wide at worst | Deep and track wide |
| External Definition | Sealed road | Gravel road |
(1) Typical values
(2) Inferred from the wiki definitions of tracktype and smoothness
(3) Deficiencies, if exist, are not corrected
(4) When present or possible
Edit 1: clarified the origin of the smoothness values following the SomeoneElse’s comment.
Is everybody comfortable with these profiles?