Here is the full list of all 19 Race.a.bit achievements.
Win bronze medals on at least half of the official tracks.
Win a bronze medal on at least one official track.
Win bronze medals on all official tracks.
Win gold medals on all official tracks.
Upload a track you created.
Upload ten tracks you created.
Upload twenty tracks you created.
Beat a friend on a track you created.
Race on ten community tracks.
Race on fifty community tracks.
Race on a hundred community tracks.
Rate a community track.
Rate twenty community tracks.
Rate fifty community tracks.
Fall of the edge.
Explode.
Challenge a friend.
Rank in the top 10 of a highscore list.
Unlock all achievements.