Ginni, is the tire beaded on the rim properly? Look for an even reveal at the edge of the rim to a point on the tire around the entire circumfrence, both sides. Lots of times there will be a variation there. It's easy to correct. just put a coulpe of pounds of air in the tire and sort of do a pinch/roll with your hands to get things even. Once all is copacetic then reinflate the tire a bit at a time checking things as you go. Should cure the eccentricity problem.
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