Brake components generate a huge amount of heat. All the energy in your trailer moving down the road at 65 mph must be absorbed and dissipated by the drums and shoes. If the drums are machined properly (consistent thickness) they absorb and dissipate consistently. When machined inconsistently the different thicknesses have a different capacity to absorb and dissipate. This stresses the shape and you end up with out of round drums. Nothing to do with balance, everything to do with proper operation of the brake system.
See? And that's exactly why these forums are so valuable. What a great wealth of information and even better, everyone's willingness to share their knowledge and experience. Thanks everyone!
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