My misunderstanding. A smaller diameter is the reason. These are some points of reference.

The Goodyear number has the nominal diameter following the R. A 1R11 model designation is a nominal 11" diameter. It could be 10.5" or even 11.25"

A 10.5" diameter (actual) has 86 square inches, so to lift 14,000 two air springs need to be pressurized to around 81psi. (81 PSI X 86 Square inches X 2 air springs) will start to lift the front.

An 11" diameter (actual) has 95 square inches so to lift the front it only needs about 74 psi.

These are theoretical and it is likely the effective lifting surface is less than the diameters given above and the diameter in the Goodyear part number probably references the outside diameter of the rubber bellows which expands a little when inflated.

My point however is that as you can see from the above even a small reduction in the diameter has a large effect on the pressure required to lift the bus. Until those buses with problems lifting the front get air springs of sufficient diameter there is nothing short of increasing pressure that will make them lift. Why one bus will lift and another will not depends upon how much weight is to be lifted. If the front axle weight is heavy, more pressure is required to lift.

There are only two concerns when selecting an air spring. Prevost, for some unknown reason has chosen sizes that do not perform as the original air springs have performed. Prevost appears to be concerned about the same things we are, but to less of an extent for bus leveling.

As long as the air springs do not interfere with anything, such as rubbing the tire or any other part of the bus the size is acceptable. That means if you are not satisfied go to a larger air spring as long as the increase in diameter does not rub anywhere. The second, and equally important concern is that the air spring has no less travel than the suspension has.

This site http://stengelbros.3dcartstores.com/...Lobe_c_62.html is as good as any that I have found to research for larger air springs.