You should check to make sure that your axle is seated properly in the dropouts (although this usually results in seat stay rub not chain stay). Also if the tire is seated properly but only rubbing intermittently on one side the tire may not be seated properly or you might need to true your wheel. If the tire is rubbing consistently but only on one side you may need to have your wheel re-dished. If none of these are the case and it is rubbing on both sides it's just too damn wide and you should trim the tire and probably not buy ones that wide again for that bike unless your into spending quality time with your tire and a sharp knife.