The only explanation I could get was that CP rated tyres are reinforced, particularly on the sidewalls, to help prevent degradation when standing for long periods. To achieve this Michelin say they have to be kept at max pressure i.e. 80psi. I will be switching to Continentals next time as their camper tyres can run at lower (more comfortable) pressures. One option might be to run the Michelins at the equivalent C rating pressure on the road and pump them back up to 80psi when left for long periods ?
Michelins approach makes sense for the typical Motorhome user I would say ...
How many people actually check their tyre pressures on a regular basis and/or adjust them for differing loads and circumstances (very few. Cue the "you should check before each journey and weekly" responses, but we live in the real, failed, world).
And what proportion of Motorhomes spend 90% of their life stationary on a driveway or storage facility - and 90% of the remaining 10% stationary on a Campsite? (the great majority of them I reckon - just need to look at the mileages of ones for sale ... 10,000 miles on a 10 year old van for example).
For THOSE users, the features of the Michelin 'Camping' spec tyres seem right and maybe the design of these tyres means they should actually be run at 80 PSI in use as well as when parked?
I don't know. Does anyone other than Michelin? Why should an individual user know better than the maker of the product? Michelin will say nothing other than 80PSI. They presumably have a reason for this stance I would imagine?
FWIW, I use Michelin Aglis Tyres on my Motorhome, but I run the Aglis Cross-Climates as they are (IMO) much more suitable for my location, being all-season tyres. The Aglis Camping Tyres are designated as 'Summer' Tyres. Come the Winter - or in Scotland, most of the year (seriously) - when average temps fall below 7C, the use of Winter Tyres is recommended, and this is where the Cross-Climates come into play rather than having to have 2 sets of tyres. It is not just about ice and snow, but temperature as well.
The Aglis Camping Tyres again are designed for the typical Motorhomer - the ones that only use their vehicles in the summer and usually head to warmer places to boot. All-year users should (again, IMO) look to fit all-season tyres.