PSI when using higher load range tires.

TheOMB wrote:
I learned sometime in my late 20's that my grandfather taught me wrong to air tires to PSI on tires. We air to the spec written on the door of auto... So that's what I've done with trailer but since I upgraded load range I wondered.

Your Grandfather was right for the times he lived. And he was just talking about car tires without changes to size or load range. Air pressure was far more important in the days of bias ply tires or even the early radials. Pressure would have a greater effect on ride and tire wear back in those days. Filling to sidewall max would give the car a harsh ride and wear the center tread significantly faster.

Today's modern radial is far better at holding the tread flat with steel belts and the sidewalls don't stiffen as much with a few extra pounds. I prefer the handling and firmer ride with a bit more pressure and have no tread wear issues.

Trailer tires (ST) tend to recommend max pressure in most conditions. Only time to air down to the pressure chart would be to resolve a handling or ride issue. This is different than what is done with car tires. Fully inflated will give the maximum load rating and probably a small increase in economy.

The tire world has changed some since Grandpa's day.