Hmmm.  I don't do much animation but I would think putting in some key frames as the wheel just touches the log, then olace your rotational hotpoint on the back axle so you can rotate the vehicle while keeping the rear wheel on the ground, then another hot point when it is rotated and lace it so the front wheels roll up to the top of the log.  Then reverse the procedure for the downward roll and do the entire sequence again for the back wheel.  If Anyone thinks this is wrong let me know.  I haven't tried anything but simple aircraft flybys up until now.