I have been told that tires while in motion generate a compound that protects them from UV rays. Sitting, as most of coaches do, and they aren't on the road daily, weekly, monthly like a charter coach, the UV devil will decay the rubber. Parking your coach indoors will help slow this process, so I follow the 7 year rule that is also not documented.
Our coach is a 1999 shell, and we just spent $$$$$$$$$ at Prevost Factory sevice center in St Nicolas, Quebec. We replaced many rubber products under the coach, rubber bushings, ball-joint boots, etc. These things didn't decay over night or even since we were last at Mira Loma---January 7, 2007. But no one there in January said anything other than all looks good after the grease job. Hmmmm.
The last we need to do is "A" arm bushings.
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