You have received several good suggestions on what to check for regarding sizing:
- Rim/Wheel Width?
- Rim/Wheel Size Diameter?
- What size is currently utilised in all locations?
There were several omissions:
- What is the recommended Tire Size at all locations from the Manufacturer Owner Manual?
- What is the actual weight of your rig per axle as determined by a weight scale?
- What is the additional weight that you plan on adding to the Rig, including cargo/luggage, people?
Once you find out what Wheel Sizes you have and what the recommended sizes for your Rig is, and the actual weight per axle, then you will be able to determine what Tire Size and Load Range will meet or exceed your needs.
Over-loaded and under-inflated tire pressure are the same thing. Suggest you purchase a Tire Pressure Monitor System that will capture the pressures of each of the tires on your Rig PLUS the tires on your Toad. This will prevent a catastrophic failure of a tire due to over-loading/under-inflation, which may be 2-psi too low! If you suffer a blow-out at speed, tire fragments will cause extensive damage to the body and undercarriage as well as loss of control.
One additional thing: tires on RVs rarely wear out from mileage, but rather must be replaced due to age. They suffer from dry-rot as evidenced by minute cracks in the side-walls and tread. Tires should be replaced at 5-years from date of manufacture. So, ensure that the tires that you purchase have a manufacture date that is within 3-months of your purchase date so that you will have 5-years of usage. The tires that you have on your Rig now are way too old and are quite dangerous!
If you are a Family Motor Coach Association (FMCA) member, you can get a tire discount from Michelin which includes Continental and BF Goodrich. The BF Goodrich ST230 is a solid Bus Tire with good sidewall protection for those curbs that jump out at you on turns.
Remember, Tires, Suspension Parts, and Brakes are the most important safety features of your Rig and a failure of any one item can be catastrophic! So, buy the best quality.