Originally Posted by gljurczyk
herk, I 'm confused are you saying that you run your tires under the cold PSI recommend? I always thought that the tire needed to be at the rated PSI, if for nothing else the wear pattern from being under inflated...
"Under/over inflated" is based on the ACTUAL load on the tire. The camper placard pressures are based on the maximum gross weight the camper is rated at. If you are loaded to the GVWR and the placard says 50 PSI and the tires are rated for their maximum load at 50 PSI; then that is what you should run.
IF (and I say again WEIGH your camper!) you have less than the rated load on your tire, THEN running the maximum PSI will result in an "over hard" tire.
This results in a "ballooned" tire and a smaller tread footprint; center tread wear; and a hard, bouncy ride for the camper.
Overloading (or under inflating for the actual load) the camper's tire (even at max PSI) will result in a squashed tread footprint with a lighter pressure in the center of the footprint and the majority of the tire's load on the edges (inner and outer side tread wear), insufficient sidewall strength to resist road debris impact, a "squirmy" ride, and the potential to roll the tire off the rim in a hard pivot turn.
"Optimum" tread contact (even pressure across the footprint) is obtained at the exact cold inflation pressure for the actual load on the tire. It will allow optimum pivot turn performance, minimum camper bounce (less broken dishes!), and a lower rolling friction resulting in better fuel economy (although harder is better here - see above for the over hard tire downside).
Manufacturers run tests on their tires to determine the optimum pressure for each load the tire is rated for (up to the maximum for that load range).
They publish this as a chart (see other posts).
Upgrading to a load range higher than shipped allows you to use exactly the correct cold inflation pressure for your load AND increase that pressure up to 10 PSI (no higher than the rim rating) to increase the speed rating of the tire.