Here is the full list of all 12 Jet Car Stunts achievements.
Get a silver medal.
Get a bronze medal.
Get a gold medal.
Beat your own ghost in Time Trial level where you already have gold medal.
Complete Platforming Hard A under 0:50:00 with no retries.
Beat the time of 1:48:00 in Time Trial Easy A.
Beat the time of 2:26:00 in Time Trial Intermediate C.
Beat the time of 4:25:00 in Time Trial Hard B.
Complete all Time Trials.
Complete all Platforming levels.
Complete all Puzzle levels.
Complete Platforming Impossible A without Retries.