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Forgot to mentionโฆ.
If one is replacing bearings/seals on existing axle, have a serious look at tire wear, tire condition and its leaf spring parts as well. If tires are wearing funny (which is a sign of bent axle or being over stressed), other parts are too rusty or one's "inner voice" kicks in, then seriously investigate the need for larger axle size as well. IMO, many trailers (big and small) are built with minimum axle size and minimum tire size ratings. For example, a 3,200 lbs axle under loaded PUP that weigh's 3,100 lbs. If your PUP needs more than bearings / seals maintenance, seriously consider upgrading to larger size axle as well. For example, replace existing 3,200 lbs axle with brand new 3,600 lbs axle (which is next size up) - for buffer on those double railway tracks / roads with extra deep bumps.
If wondering, I just replaced the 2 x tires/rims under my boat. They were factory ST185/80R (C rating) and after lots of research, I replaced rum/rubber with ST185/80D ("D" rating) - which gives me 300 lbs "more" strength per tire. That's 600 lbs of extra "buffer" - for those double railway tracks and extra deep bump road abuse. If one's PUP also needs new rubber, do consider replacing with "next size up" rims/rubber as well.
Another TIP: If your loaded PUPs weight is more than Tow Vehicle's Cargo Capacity, I'd recommend installing brakes under your attached PUP as well. In my region, trailer weight before needing brakes is 3,000 lbs. My mini-van's Tow Vehicle's Cargo Capacity (meaning, how much weight within its rear cago area) is 1,500 lbs. Each of my trailer's rated to pull more than 1,500 lbs NOW has brakes. By comparing BEFORE and AFTER braking power, I'm now a firm believer that braking laws in my region should be changed to 1,500+ lbs. Meaning, their comparison of before and after is a NO Contest comparison. Especially when trailer brakes are installed with STAR wiring design. Long mumblings shortโฆ If one's PUP is more than 1,500 lbs and attached TV's max cargo capacity is 1,500 lbs, then DO install brakes under the PUP as well. It's well worth it. Especially if replacing with much better axle at the same time.
Hope this helps as well..