Originally Posted by maniac57
Place the uneven rubber inside the rim and away from the sprocket so it sits flat, But spacers should help if thats the only way. You could also try cutting your own from old tires or something. A hole punch set is fairly cheap or you can make one from a sharpened bit of tubing. Even in the wilds this should be practical.
Thanks maniac for the reply. I disassembled the rear sprocket and moved the inside rubber to the outside under the sprocket and then cut out a piece of inner double thickness to put under the inside rubber where it was thin (about a quarter of the disk). Then re-assembled and finally got it true! But then I saw I needed to flip the sprocket! Oh well, an hour and a half later it was done...and it is so great now! Took it for ten mile ride mostly uphill, no problems at all.
Chain/sprocket alignment has to be the most critical part of these motorized bikes.