Here is the full list of all 18 PolyRace achievements.
Create 1 challenge
Be in the top 3 in the race of the day
Finish time attack / normal race with no hit, no brake, boost always activated
Be in the top 10 in the race of the day
Finish time attack / easy race with no hit, no brake, boost always activated
Win 1 challenge
Win the race of the day
Win 10 challenges
Win 20 challenges
Win 50 challenges
Win 100 challenges
Create 10 challenges
Create 50 challenges
Create 100 challenges
Finish time attack / hard race with no hit, no brake
Finish time attack / extreme race with no hit, no brake
Unlock all missions
Get 5 stars on all missions