Having read this thread, I have one question for all. Has anyone considered looking at the side of the tire?
They put a recomended air pressure there for a reason. If it says 90psi, put 90psi in it. It's not designed to be run on less.
Under-inflation causes crowning(outer treads wearing faster than inner treads), excessive heat generation and, in extreme cases, belt damage. this happens whether the tire is under a load or not.
Over-inflation causes cupping(inner treads wearing faster than outer treads), reduced traction under break and on wet surfaces and, in extreme cases, belt damage. This happens whether the tire is under a load or not.
The most common cause of blow-outs is under- or over-inflation.
There is a reason that recomended air pressure is branded into the side of your tires. Look at it and use it.

I think YOU might want to re-read the sidewall. Usually it says- MAXIMUM PRESSURE or words to that effect. That means do not exceed the printed pressure no matter what weight is on it. For lighter weights, lower pressures ARE permitted, and usually recommended by the tire makers themselves for longer tire life. Using maximum pressures under very light loads as discussed here will NOT lengthen tire life, and will make the ride much rougher because it cannot cushion bumps.

Joe,
I found something on Michelins site that might help.
Go to https://www.michelintruck.com
Hover on products. A sub-menu will open. Hover on New Tires and you'll get another sub-menu. Click on new tires. Enter the info that best describes your application and click continue. Click on one of the resulting tires and on the page that opens, find the button that says Load and pressure. This will give you a chart showing the minimum air pressure at a given load.
Keep in mind, if you run "Drive" tires on your drive axle, instead of "steer/any position", they won't be listed under recreational vehicle. You'll need to look under "Truckload Carrier".
Having read the chart, it seems the minimum recomended air pressure for an 11R22.5, if you are running "drive tires" on your rear axle and the load is 17,520lbs or less, would be 70psi. 75psi. if the load is between 17,520 and 18,320 etc.
The pressure/load is different for metric tires. Also different for "steer/any position" tires.
Hope this helps.

Gary,
My last statement wasn't intended as an attack. Sorry if I offended you. It was meerly a word of advice.

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Gary,
My last statement wasn't intended as an attack. Sorry if I offended you. It was meerly a word of advice.<HR></BLOCKQUOTE>
Don't worry. I didn't take it as such. My only point was "one pressure fits all" is not true. Different loads require different pressures, up to the maximum stamped on the tire. Take care!

How does low usage and long non-usage factor in?.....geof

Thanks, James. I looked over the charts. It looks like I can get away with 70 psi in my front (steer) axle tires if I'm under 9,000 lbs. 70 does seem a bit low to me (for no scientific reason). I have 90 all the way around and the Volvo rides kind of rough (bobtail). So, I think I'll back them down to 85 and see what happens. Joe

1998 Volvo VNL64T610 N14Cummins