Several years ago when we had our 2002 XLII Marathon one slide, we explored the larger sized tires. (365's) They said we would have smoother ride, since for our front axle weight the pressures would be around 20 psi lower than the OEM 315's. so we would have run about 105 psi up front.
It would have required the new tires X 4, new rims X 4, and new sealed greased hubs X 4. Plus the labor to do it, we were quoted around $8,000.00. Along with the fatter tires, the newer shells have larger front air bags that inflate with lower pressure as well. This enhances the smooth ride of the 365's. Problem with mounting the 365's on a coach that didn't have them to start with, there is a static turning difficulty. The newer shells have a "Slave Cylinder" on the drag link to aid in static wheel turning. A friend ours in Coach 726, a Marathon 2002 "H" placed the large tires on his coach and now he is unable to turn the steer tires in place. He must roll the coach to turn. The wider footprint has more pavement friction.
It is a cheaper way to update an older coach, than buying a new one.
Jim and Chris
2001 Featherlite Vogue XLV 2 slide with Rivets-current coach, 1999 shell
Previous 22 years,
We have owned every kind of Prevost shell but an H3-40