Here is the full list of all 10 King Of Dirt achievements.
Make 500 stunts
Make 5 backflips in one line
Make 5 stunts in one jump
Make 5 barspins in one line
Paint your bike
To get to the finish line
Make 50 stunts
Make 5 tailwhips in one line
Make 10 tricks
Make 3 stunts in one jump