There is a very easy way to go up in tire size slightly for slightly better fuel economy and more ground clearance without changing your rims and without worries of the dually sidewalls rubbing.
Go "up" to 215/85R16 tires of the same Load Rating as your current 225/75R16 tires. I ran stock 225/75R16 Load Range E tires on our Class C motorhome for several years before switching to 215/85R16 Load Range E tires around 3 years ago. The 215 tire actually has about a 1.2 inch larger diameter than a 225 tire, so all gears are just a bit "taller", for better mileage. Load Range E is Load Range E, so both tires can carry identical maximum loads. A 1.2 inch larger diameter provides 0.6 inches higher road clearance for the entire vehicle, including all suspension and drive components and all coach components. The 215 tire is slightly narrower than the 225 tire, so spacing between dually sidewalls is wider to better guarantee no sidewall rubbing and there is another advantage - more air flow between the dually sidewalls for improved cooling of the tires in hot weather travel. Also, another advantage seldom talked about is - at any given loading - reduced tire tread wear when tire diameters are increased.
Of course I had to buy seven (7) tires at replacement time (a new spare, too) to change to the larger diameter tires, but I need only buy six(6) from now on. I now use Michelin LTX M&S2 215/85R16 tires.
Any loss of power from the larger diameter is insignificant, since we have an E450 chassis under our small (24 foot) motorhome instead of an E350 chassis. The E450 has more pulling power due to it's lower rear differential gear ratio, slow larger diameter tires have no effect that we can feel when pulling grades. The speedometer now has about a 1.5 MPH under-speed reading error at cruising speeds, but that is of no concern to us.
I have run over-stock-diameter tires on some of my vehicles for years with no negative effects whatsoever.
2005 E450 Itasca 24V Class C
