Another thing is although these 16" tires are the same overall diameter as the old bias ply 700R15's, they are a different shape. The old bias ply tires had a pronounced roundness to the tread area, whereas these tires are pretty flat. So that inside tread edge is sticking out further up a little higher, probably a good 2" higher. Just a thought.
One way to know on the extent of movement on your torsion axles is to just back your trailer up on some boards so the rear wheel is off the ground and the front is supporting all the load for that side. It certainly won't hurt anything to do so and I'm guessing that would replicate the movement arc of the axle. You can look and see, but it will hit a hard stopping point in the upward arc. If your axles are sagged, then it will probably be surprisingly close to the starting point in their "resting" state. You'd be able to check for rubbing without causing any damage.
Dallas Peak, MD 'That 70's Guy!'
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