Very peppy, uplifting happy songs.
+1...
Nothing exhausting, tiring, distracting, occupying your mind (like classical music or tracks like J.M.Jarr?, as much as I love them on my audiophile home stereo...)
Also nothing too metal, too belligerent, which doesn't make you "faster", only "aggressive" thus skittish and squarish...
A quality reproduction, and not just screaming, beyond recognition compressed MP3's...
Also the lyrics shouldn't be to "heavy" or too dark... (in this some happy sound tracks from Mike & The Mechanics, Bruce Hornsby or Chris Rea
can already be borderline... ;-))
I run anything from the 70ies till today, as long as its good IMO... some AC/DC, some ZZ-Top, but nothing super heavy like Judas Priest... rock, pop, dance, anything... Billy Idol, Bob Seger, Springsteen, Bryan Adams, The Corrs, Flash & The Pan, Genesis, Rafferty, Huey Lewis, Icehouse, Manfred Mann, Men At Work, Nickelback, Robert Palmer, Texas, etc, etc...
Set to random-shuffle the +500 tracks will last for weeks of riding...
Some good old ballades have a slight dangerous effect on me, I can get really smooth and really fast on tracks from Journey or such...