Tires: Rear tires, rear tires, rubber dust

Question
on dualie ie two tires per side of rear axle: how exact do the tires need to match? I had put 2 tires together both with same size noted on sidewall and after about 200 miles when I stopped for fuel on my walk around I noticed black rubber dust on the back of the rv then noticed on that same side the inner tire had wore down to the cords.What happend?

Answer
Mark,

On dualled tires, they need to be almost exact - and the less exact they are, the more likely there is to be problems.  

This means the same size, make, and model, and state of wear.  I've heard that you shouldn't mount up tires that are more than 4 /32nds of an inch different in tread depth - keeping in mind that we are talking the same identical tire except for the amount of treadwear.

I've also heard that the diameters have to be within 1/4".  Also keeping in mind twe are talking the same size, make and model.

But both of those things I can not seem to find documentation even though they seem to line up very closely.