The other thing I read in the trailer owners manual is that we have "sealed bearings" which can't be repacked. You have to replace the whole hub. See if there is any movement when you lift the wheel off the ground, and wiggle it side to side and top to bottom. I've had bearings last 100,000 miles and the replacement didn't last 10,000. Whoever came up with this idea should have the fleas of a thousand camels infest their nether regions. I've never heard of Zieman but if you like that brand, go for it. We are lucky enough to have a company open up here that builds trailers from thick wall aluminum stock, and we can order it with the options we want. Cupping may have something to do with balance, and it's hard to catch an out of balance tire on a trailer if it isn't way out. Also check the fasteners that hold the axle to the trailer to see if there is any loose hardware. Good luck, and let us know what you find. Tom