i have a rear tire that will not seat perfectly on the bead it does this slight wobble been riding it as a xc bike didn't do much to fix it. I am getting a new bike soon. Ive checked the wheels for trueness and they are its just the tire. it could be mis molded or it could be not sitting on the rim perfectly. put a zip tie with the leader touching the rim on the seat stays spin the wheel check for wobble.