Q. We have a 35-foot motorhome with 19.5 wheels, and I generally drive 400
to 700 miles a day when traveling. How much air pressure should I use? The sidewall on the
tires calls for 90 psi, but traveling that far on a hot day will increase the pressure 10
or 15 psi. Should I lower the pressure, or is it safe to use 90 psi?
The 90 psi on the sidewall is for maximum load. If you don’t know how much weight the tires
are carrying, the safest thing to do is run the maximum rated pressure. However, the
preferred way to set pressures is to weigh each corner of the coach, then look up the tire
manufacturer’s recommended pressure for that specific weight. Truck tires have a 10-psi
margin above that so that you can over-inflate (in your case up to 100 psi) to allow for
natural pressure loss over time. Always set pressures before driving. Never bleed off air
pressure when the tire is hot. You can find the load/inflation tables on the tire
manufacturer’s Web site or at tire dealers. They vary between brands, so be sure to use the
correct one. On rear dual wheels, divide the corner weight by two to get the individual
tire load, of course.