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