Tires: switching tires and rims, rim widths, rim width

Question
Hello. My 1974 dodge class a motorhome,front disc brakes rear dual drum brakes, 10,000 to 14,000 gvwr with michelin 8r19.5xza tires convert to a 225 70 19.5 tire and new rim. My tires are out dated so I am changing them anyway. I would go with your advice regarding rim width that Icould use and possibly going with a 245 or up tire. Iam ok with the speedo being out because I use gps when driving. Thanks Al.

Answer
Dear Alan,
Thank you for using AllExperts.
Am I to understand that you have already converted to 225/70R19.5?  
If so, the suitable range of rim widths for this size is 6.0" to 6.75". As you have provided the GVWR, the load capacity of the 225/70R19.5 12 ply (load range F) is:
1,650 kg @ 95 psi, or 3,640 lbs. @ 95 psi per tire (single)
1,550 kg @ 95 psi, or 3,415 lbs. @ 95 psi per tire (dual)
I'm not sure if your rear tires are in dual. You can let me know.
A 245/70R19.5 12 ply would require a minimum 6.75" rim width and may be mounted on a rim width up to 7.5" wide.
Load capacity for the 245/70R19.5 12 ply:
1,850 kg @ 95 psi, or 4,080 lbs. @ 95 psi per tire (single)
1,750 kg @ 95 psi, or 3,860 lbs. @ 95 psi per tire (dual)
Warning: The wheel must be rated to carry the maximum load of the tire.
Overall diameter comparison of tires:
8R19.5:  33.1 - 33.3"
225/70R19.5 = 31.93" (highway tread)
245/70R19.5 = 33.03" (highway tread)

DT