Tires: RV Tires, rv tires, class c motorhomes

Question
Hello Barry
I am an RV technician 2nd level apprentice and am working for an RV rental Company with Class C Motorhomes.Since inflation of tires varies according to different loads(this may be elaborate to explain to the renter)what could be considered a "rule of thumb" for inflating pressure on a tire that says max 80 psi cold for example.The vehicle manufacturer(Ford 450) has a sticker on the door side stating pressures at 60 psi rear and 65 front?

Answer
The rule of thumb is to go by the vehicle placard (the sticker).  That's because the vehicle manufacturer spent a lot of time deciding and testing to make sure that inflation pressure worked for the vehicle.  BTW that pressure is only applicable for the original size tire.  It would be the same regardless of the manufacturer of the tire, but change the size and you change the load carrying capacity for a given pressure.

I know you were hoping for "85% of the sidewall" or something like that.  Unfortunately, there are so many exceptions that anything other than "the placard" just flat isn't good enough.  Plus the placard should be easy to find.  In a few years, a new law goes into affect and the placard will be required to be in the driver's door area.  I'm not sure where it's supposed to be if there isn't a driver's door, but whatever the new law says, it will be basically the same location regardless of the vehicle.

Hope this helps.