Originally Posted by fast murray
I'm reasonably sure that it has a D stamp on it. It is rated at 2150#, the others had a D stamp but were rated something like 2450#. The only thing I can come up with is the tire supplier mistakingly had them together and delivered them to the tire dealer that way and along the way nobldy noticed. Appearancewise, they all look the same. Even after I discovered the cupping and the rated max pressure, I sat there staring at the 2 side by side and couldn't see any difference. I can't wait to get them home so I can look again. Maybe even post a pic.
As far as tread goes, the tires will look identical...it's in the composition where there is a difference.
From everything you have posted so far, I have a feeling you have bias (or non-radial) tires installed.
When you say all the tires have a D on them, is this D listed in the size of the tire? Example ST225/75D15.
If that is the case, that D is not a Load Range (although many people do confuse it).
The letters you see in the size, state the construction of the tire as follows
R = Radial construction
D = Diagonal construction
B = Bias construction
D and B (Diagonal and Bias) mean the same thing, as some manufacturers will use a B and some will use a D
You will need to look along the sidewall some more (not in the size) and you should see something like "Load Range" or "LR" or "Ply Rating". There will be a letter code after these words that tell you the ply rating of the tire. It may also just flat out state the ply rating with a number (6,8,10).
C = 6 ply and 50 psi pressure
D = 8 ply and 65 psi pressure
E = 10 ply and 80 psi pressure
Now there also exists the possibility that a tire got molded wrong in the manufacturing process. It could be a 6 ply tire, that got an 8 ply Load Range molded on the sidewall (or vice-versa)
I just have a feeling that you have bias/diagonal tires, as they are more prone to the problem you say you are having also. I do believe you have some kind of axle problem too, since you stated the tire is only wearing from the middle of the tread towards the inside of the tire. It is also easy to damage/bend something when you jack it up....and I am tending to believe this happened when they repaired your brakes.
Check out this link, and see if the pictures shown reflect your condition.
and you can scroll down the page from this link to read about cupping/feathering problems on rv's.