On our previous coach, our 255/70-22.5 G670s worked just fine for about 30,000 miles. However, around that time, both front tires started "rivering" (small scallops on outside edge of the tread) and proceeded to get worse in the next 5000 miles. I could not tell any difference in the handling aspects, and I never had a problem with loss of air. We sold the coach with the tires on it and I understand that the dealer put new tires on it before he sold it.
There are a lot of posts here on rv.net about these tires...do a search on "G670
and read them.
Ron