Here is the full list of all 38 Riff Racer - there are Race Your Music achievements.
Unlock ALL packs
Unlock 20 packs
Reach Driver Level 20
Reach Driver Level 15
Reach Driver Level 10
Drive ALL cars
Drive 10 cars
Unlock 10 packs
Play a single song 10 times
Drive 100 songs
Drive 50 songs
Play a Classical song
Drive 5 cars
Unlock 5 packs
Play a Hip-Hop/Urban song
Reach Driver Level 5
Score more than 100,000 on a song under 3 minutes in length
Drive 25 songs
Jump more than 8 beats in one manoeuvre
Play a Pop Song
Beat a friend's ghost
Stay in the super-sync zone for 25 consecutive seconds
Race on a song longer than 10 minutes in length
Smash 30 boxes or more without missing one
Boost 20 times or more in one song
Play a Jazz/Funk/Soul song
Enter the super-sync zone 10 times in under 40 seconds
Drift more than 16 beats in one manoeuvre
Play a Rock/Metal song
Beat a recommended ghost
Drive 10 songs
Author 10 tracks
Author 5 tracks
Roll more than 4 beats in one manoeuvre
Stay 100% in sync for a whole song
Drive a whole song without hitting a barricade
Play a Dance song
Author 1 track