So going through the Goodyear RV literature and I see that the 670's have a 5 year warranty and the 647's are 4 years. That says something to me.
And I have the 245-70R19.5 size and in the load chart, those size tires made after 2/28/06 need to be inflated 10 psi more for the same load than tires made before that date. Boy, that is convenient... and that applies to the 670's also.
Any problem putting a pair of new 670's on the front and taking the good 647 steer tires to the inside dual position so I end up with 3-5 year old 647's on the rear, all with about equal wear (and diameter). All of the 647's are in good shape with less than 10k miles. I will of course have the tire tech go over them first.
Ole and Anne Anderson, Highland, Michigan
'02 Adventurer 32V, Ford F-53, ours since 4/08,Goodyears, Konis, SeeLevel, CHF
'84 CJ-7 , 5.3 Chevy, 3" lift, 33's, Detroit Locker, Fiberglas tub, winch, hi-lift