I did some research on this - as my coach has 295/80R22.5 on Drive and Tag, and 315/80R22.5 on the front. Installed by previous owner. He said he went to the 315s because they can handle more weight.
The 295/80R22.5 tires are 41.1 inches OD (that is 491 rev/mile), and 11.6 inched wide. The load capacity is 7,830 lbs. (load range H)
The 315/80R22.5 tires are 42.3 inched OD (477 rev/mile) and 12.4 inches wide. The load capacity is 9090 lbs (load range L), however if they are mounted on the stock 8-1/2 wide rim Michelin has de-rated the load capacity to 8,000 lbs. So not as much difference.
I carry a spare tire (a 295/8022.5) so I was thinking of going back to the standard tires sizes on all axles, then my spare can go on the front axle if needed and I wont have mismatch on tire sizes. Someone was commenting on that, and said the wider tire width of the 315 still makes it desirable to keep on the front as the larger tire contact area gives you better handling (less chance of skidding I guess) - That makes sense, so I'm not sure what I'll end up doing (I've got a couple of years of tire life to go).