Touring - tire pressure for touring

i recently purchased a kona sutra. it comes with iso standard 584 diameter wheels. i have looked into this size wheel and apparently it is not very common. as a result there is a lesser selection of tires that fit these wheels. none of them can be inflated to more than 85 psi. is there something i should know about? im used to riding road bikes where the minimum tire pressure by my standards is 100psi. is it preferable to have less air in your tires when carrying heavy loads? if so...why?

What's the actual tire size?
Wider tires generally take less air to fill them than thin road bike tires.
I put about 55#'s of pressure in my 26x1.75 tires.
On my hybrid bicycle I think I ran around75#'s of pressure,those were 700x35.

Put enough air in them to not get pinch flats.

the non iso size is 26 1/2

85 psi is fine. I ride a tourer with standard 700mm wheels and use 32 mm Schwalbe marathon plus tyres, because they're virtually puncture-proof. They have a maximum pressure of 90psi, and I doubt if I'd notice the difference between 90 and 85. They roll fine, even fully loaded. As a general rule, the bigger the tyre, the lower the pressure needs to be.

85psi is good, but 100psi is better! Only my opinion, but lower rolling resistance is always nice on long tours.
You know what they say about opinions though "they are like armpits--everyone has a couple, and most everybody ELSE thinks yours stink!"
That said I also have 26x1 1/2 tires, but on ISO559 wheels. After looking around a fair bit, I found Schwalbe Marathon 100psi max tires that work very well. The difference between 85 and 100psi might not be a lot, but I am willing to take any help I can get! It just makes it a little easier to get back on the bike the next day.
One advantage of lower pressure is riding on dirt or gravel--a little less (say 80% of max) helps tires roll OVER loose surfaces, instead of through them. Just be careful not to overdo it--beware the dreaded 'snake bite'! And be sure to "Pump It Up" once you get back on pavement.
If you REALLY want higher psi tires, you may have to get new wheels. This would also simplify finding replacement tires--at home and on tour, should you ever find it necessary.
As always, you should decide what works best for YOU, in light of (or in spite of) all the advice.

Narrow road tires need higher pressure to stand up under load. Larger tires need less pressure to carry the same load due to their greater air volume--the 'cushion' effect. This also provides a more comfortable ride, since the larger tire can 'soak up' smaller bumps and road irregularities.

Ideally you want to fill your tires to the pressure where they deform (drop) by 15% of their thickness when loaded. That pressure will vary depending on the load and how it's distributed. This article by Jan Heine in Bicycle Quarterly (http://www.vintagebicyclepress.com/images/TireDrop.pdf) gives Frank Berto's calculated figures based on the width of the tire and the weight on it. Highly recommended. In other articles (not available online), Jan examines real-world rolling resistance, which is often very different from the figures that tire manufacturers obtain by rolling their tires on smooth steel drums.

On my Surly LHT, with 35mm tires and a moderate load, I run the front tire at 55 psi and the rear at 75 psi.

Things got complicated: the Sutra comes standard with Mavic A317 which are 700c wheel, like most others on road bikes. As pressure goes it has been demonstrated that a 15% drop of the tire, loaded is the optimal compromise between comfort and rolling resistance: please read (http://www.vintagebicyclepress.com/images/TireDrop.pdf).

i recently purchased a kona sutra. it comes with iso standard 584 diameter wheels. i have looked into this size wheel and apparently it is not very common. as a result there is a lesser selection of tires that fit these wheels. none of them can be inflated to more than 85 psi. is there something i should know about? im used to riding road bikes where the minimum tire pressure by my standards is 100psi. is it preferable to have less air in your tires when carrying heavy loads? if so...why?
I used to think that higher pressure and (theoretically) lower rolling resistance were important. Over the years, my thinking has changed. Lower pressures have their advantages. Sheldon Brown deals with this issue well -- you can probably still find his writings on the subject online.

I found the higher pressures to be overrated. They cause more fatigue over long hours and days of riding. Also, over some surfaces the lower pressures are definitely more efficient.

The ideal pressures for you would depend on a variety of factors. If you experiment, and go by empirical or experiential results rather than theoretical ideas about pressure, you'll probably arrive at something more experientially satisfying.

I run 700x32 @ 65 psi front, and 700x28 @ 70 psi rear. Why so low? Because the average speed penalty is only 0.5mph vs. the higher 90 psi. On the plus side, I get much better traction/handling, and a more comfortable ride.

There are three major factors that limit my average speed:

1. Traffic...can't control
2. Road condition...can't control
3. Road hazards...can't control

Assuming Frank Berto was right, this spreadsheet (http://rbw-owners-bunch.googlegroups.com/web/tire_pressure_setup.xls?hl=en_US&gda=aegQfUkAAABJ1SCrFczYQJXt-kr904WwTuK4w2Z6faswomCClHsGqGDkwNCMPbfhRJBWVauzP9yabMNsgG8LJBVMrV9E7JsQhAioEG5q2hncZWbpWmJ7IQ) will tell you what would be good PSIs.