I just read something about this the other day in the mechanical forum on http://www.schoolbusfleet.com
There were differing opinions on the issue. These facts are not subject to dispute: overinflation causes excess wear on the center of a tire's tread and causes a rougher ride for the vehicle; and, underinflation causes excess wear at the tread edges and causes excess heating of the tire.
One person pointed out that the ratings on tires are the *maximum* pressure at the *maximum* load rating for the tire, and said that in the fleet he mechanics for they use 75PSI in their tires. I don't know if that's good or not, that's just what he said (as I recall it.)
One part of the discussion evolved around differing wear characteristics between tire manufacturer's products, something that would be unique to each person's situation.
Going outside, be right back.....okay, back.
My little Jeep Wrangler has 9.5" x 30" light truck tires on it. The lettering on the tires says that the *maximum* load for the tires is "1985 pounds at 50 PSI cold". I run the tires at 32 PSI, not 50. (No way my Jeep could carry 4 x 1985 pounds, at any PSI rating!) The tires wear evenly at 32 PSI. I had run the last set for a while at 40 PSI because I was driving many highway miles each day and wanted to get better mileage, but the tires ended up wearing down more quickly in the center, and so I then underinflated them to about 28 PSI for the last 20,000 miles of their life (I was still able to put 80,000 miles on the tires before replacing them.) They ended up with a really strange wear pattern, angular grooves of very worn areas all the way around the tire -- not cupping or feathering but grooves extending from one side of the tire to the other. Balance and alignment were maintained properly the whole time, so those factors were not primary causes of the strange wear.
I am not making recommendations, but it *seems* to make sense to me that if a bus is used in a capacity wherein it does not approach its maximum weight, there is no need to manage the tires as if they were carrying the maximum weight. If the GVWR for the bus is 26,000 pounds and its completed actual gross weight is only 18,000 pounds, it doesn't make sense to me (from a purely theoretical standpoint) to treat the tires as if they were routinely carrying 26,000 pounds. Advice from a competent mechanic, the vehicle manufacturer, and the tire manufacturer should all be considered in making any decision about how to manage the tires' inflation.
But as much as tires cost, it seems to be a good idea to get the most mileage out of them possible!
YMMV, I'm just a wannabe and have no practical experience. Correction and edification always appreciated.