Took a guided off-road trip from Pai that was a blast.  Highly recommend to anyone with a true off-road bike, although we slogged it through on 250 AX-1s.  North to the Burmese border and tiny villages that the trekkers don't go to.  Contact the Baantawan Guesthouse ( [email [email protected]][email protected][/email], 053-698116) just downstream of the bridge and on the River Pai.  Thip is the guide and he must know the off-road trails better than anyone around.