Q: I live in the desert Southwest and pull a 39-foot Grand Junction fifth-wheel. It is not uncommon for us to experience noon temperatures up to 40 degrees higher than the morning temps. When we travel in those conditions I start with 80 PSI in my tires as is called for on the sidewalls of the tires. By noon, after the temp change, my tires exceed 90 PSI. This makes me nervous as my wheels are rated 80 PSI. Should I gradually deflate my tires as the day warms up, or ignore the 90-plus PSI and just keep driving?
Jim Carolan, Palm Desert, Calif.
A: If the tires are LT tires, the pressure marked on the tire sidewalls is the pressure required when the maximum weight (also marked there) is being carried by the tires. It’s doubtful that your trailer weighs that much. Therefore, you should weigh the trailer axles on a truck scale (when fully loaded for a trip) and determine the weight on individual wheels and tires. Then look up the manufacturer’s recommended tire pressure, using a load-inflation chart (available on tire manufacturer’s websites and at tire shops). Set the correct pressures before driving off in the morning and then leave them alone all day. An exception is if you fill the tires at high altitude and descend, in which case the tires will need to be checked/inflated (best done after a rest stop to allow tires to cool down).
– Ken Freund