Hesitant to chime in here. Tire talk gets real emotional, real quick. But its Sunday, sermon was short, brunch was not bad. So, why not.
Our coach OEM was Michelin 255/80-R22.5. PO replaced with Dunlop 255/70-R22.5 two months prior to our acquiring. In April, we replaced the Dunlops out of an abundance of caution.
We went with Cooper Roadmaster RM272's. 255/70-22.5. Our spring trip put 3500 miles on them. Literally, rain, tornados, high winds, Arkansas ' excuse for highways and finally snow. Doing well.
Chose those because we ran those on the tractor/trailers in the distribution center of my next to last civilian job. (Aggressive work history.
Some particulars: 70s have a reduced diameter from the OEM 80s. So your odometer reads about 2.5% more miles than you've actually driven. And, your speedometer reads about 2.5% faster than you are actually driving.
Some folks say that the 80s give a bit softer ride. Don't know how to test that. But for sure, 80s normally have to be special ordered, and normally more expensive. And, for sure, 70s have significantly greater load carrying capability.
These are my opinions/observations. You'll get others.👍
Fair Winds and Following Seas.