Ok, here is the scoop on the Michelin XZE G load range VS. the XZE H load range.
I talked with an engineer today at Michelin. It seems the 275/80R22.5 G (14 ply) is standarized to the American Tire and Rim Assn. They set the standards for load inflation pressures in the US. The 275/80R22.5 H (16 ply) is standardized to a European specification. The reason for this is that this tire is speccifically built for commercial applications that require being able to carry heavier weight, particularly on the front axle. European standards allow a heavier weight at a specific PSI.
The Michelin tech said 90 to 95 percent of all tires the same size, carry the same load, at a specific PSI, no matter what load range.
So the big difference here is the US standards VS. the Euro standards.
He also made a good point, in that a reduced pressure will cause more side wall flex and tread squirm. This might result in a poorer handling coach.
So John is right on the XZE. But I will stand by my statement that higher load rating will not allow you to reduce tire pressure...in 90 to 95 percent of the tires out there!!
I'll get off my soap box now