parkmanaa - I don't see how it could be much more than 7 years since Gator Ford said my tires were "showing signs of dry rot" and they aren't even at the 7 year mark yet. My RV is even kept covered and only used for 100 mile trips maybe once a month.
Went to their website and couldn't determine chemical makeup from their pdf.
From Michelin's website:
PROPER CLEANING OF RV TIRES
Like the rest of the RV, it pays to keep the MICHELIN®
tires clean. Road oil will cause deterioration of the rubber,
and dirt buildup will hold the contaminants next to the tire.
As with the cleaning of any rubber product, proper
cleaning methods must be used to obtain the maximum
years of service from the tires. A soft brush and the
normal mild soap that you would use to clean the RV
may be used. If you use a dressing product to “protect”
the tires from aging, use extra care and caution. Tire
dressings that contain petroleum products, alcohol, or
silicones will cause deterioration or cracking and
accelerate the aging process.