Alright well lets think, its a biking trip so you'll want something intense but not to the point of headbanger. The old highway classics won't work either because you have a dirt bike not a chopper. So heres a few suggestions.
1. The Gauntlet - Dropkick Murphys
2. Wart Hog - The Ramones
3. Blue Orchod - The Whote Stripes
and of course theres my favorite out of the bunch and probably the most cliche one....Ride by The Vines....of course you can always go in a different direction, foregoing the rock and putting some trance music in, but thats a matter of taste.