If they are Bias ply tires that is a normal characteristic of how they wear. If it was smooth wear all the way around it would men it is toed in or bent back in middle of axle. This wear is probably only on the 2 outside ribs of the tire. Take wheels off and get them re mounted the oppisite direction and reinstall. Get a lot more miles before having to replace. When replacing get radial trailer tires and they will wear smooth.