Originally Posted by forester2008
I know this is an old thread, but I always thought that tire pressure was independent from the weight of the vehicle. If you over-inflate you run the risk of damaging the tires just as under-inflating them will. Correct me if I'm wrong, but temperature does affect the tire pressure, the hotter it is the more pressure increases, the cooler it is the lower the pressure. I believe you should always stick to the recommended pressure on the tire wall. ...for what it's worth...
Sorry but whoever told you tire pressure was independant from the load on the tire gave you bad info.
The tire industry worldwide follows published industry guides for the tire dimensions and the tire load capacity under various conditions. These came about in the '50s and '60 because consumers had no way to know if a 7.50-15 from manufacturer A would fit their car that had 7.50-15 from Mfg B, or carry the load etc.
In general, in North America and some South American countries T&RA, Tire & Rim Association book is used. In Europe the ETRTO, European Tyre Rim Organization book is used. Japan has JATMA and Austrailia has a book also. The "metric" country guides are almost exactly the same.
Now there are slight variations due to calculation rounding and dimensions. Metric to "English" rounds differently than when you do calculations in "English" units and round and convert to metric but these differences are not significant.
35 psi vs 36 psi or rounding up or down 5 pounds or 3 Kg for example but these are not significant.
When looking for the correct inflation for your RV tires you may find one company may publish special tables for its RV tires but again the differences will be minimal, usually only a hundred pounds or so.
If for example, you have 285/70R22.5 tires and can only find a Bridgestone chart or a Michelin chart but your tires were made by "Bob's Tire Co" and can't find a chart printed by Bob then you can go with the charts you find. If you do find a chart by Bob Co then you need to confirm the load and inflation on that chart.
#1 get your rig weighed when fully loaded
#2 get each corner weighed and look up the required MINIMUM inflation that EXCEEDS the measured load. I suggest you also go up 5 psi from the table minimum.
#3 If you can't get each corner weighed at least get each axle weighed and assume one side is carrying 55% of the axle load and use that load when looking in the tables.
#4 Remember the different capacity of Single vs Dual application
#5 Get and use an accurate gauge
#6 Check the inflation in the morning when they are out of the sun EVERY TIME BEFORE you leave your campsite
#7 Keep your tires covered to help protect from UV
$8 have a safer drive down the road by knowing you have more air than the tables indicate.