Here is my take.
First, I believe there are 2 parts to this issue that need to analyzed separately.
1)The effect of the addition of airbags to the rear axle
2)The resulting effect of those airbags to the front axle.
Related to 1) above, first you need to determine what you want to accomplish with the addition of the airbags. To explain the scenarios, we will assume the trucks weight is fixed. Using Ron's example, let’s say there is a 1000 lb tongue weight that causes 500 lbs to be unloaded from the front axle and 1500 lbs to be added to the rear axle. Basically, as a result of the added tongue weight, the front of the truck goes up and the back of the truck goes down.
With this in mind, the 3 possibilities for the addition of airbags on the rear axle that come to mind are:
A) Restore rear of truck to its unhitched ride height.
B) Give your truck a level stance.
C) Stabilize the load for ride comfort.
A) Restore unhitched ride height: The only way to accomplish this is to use the airbags to lift the back of the truck so that 1000 lbs is supported solely by the airbags. Then, the WDH would be used to transfer 500 lbs to the front axle. The only way I think you can accomplish this is if you use a scale. I say this because if you hitch up and use the airbags to level the truck before WDH is applied, you would be supporting 1500 lbs. Application of WDH would transfer 500 lbs to the front axle and the back of the truck would be unloaded by 500 lbs and possible raised above unhitched height. This may make for an unstable ride.
B) Level stance: The only way to accomplish this is to apply WDH to transfer 500 lbs to the front axle. Add air to the airbags until the truck is level. The problem is that if you stop here, you may unload the WDH. This is where I ran into “trouble” earlier in this thread, so I will try to be careful in my explanation. When the airbags are pumped up, the angle the hitch bars make with the pavement will change (or lessen), causing the WDH to unload. When the WDH unloads, weight is transferred back to the rear axle and 500 lbs is no longer distributed to the front axle. Therefore, I think the only way you can accomplish this is with the use of a scale.
C) Stabilize the load: This is my preferred method. The way to accomplish this is to apply WDH and adjust to put 500 lbs on the front axle and keep 1000 lbs on the rear axle. Pump air into the airbags until you just see the rear of the truck rise. In this case, 1000 lbs is supported by the suspension. Uneven road surface, maneuvering, bouncing, etc. is supported by both the rear axle and the airbags. This results in proper weight distribution and greater stability.
Related to 2) above, I explained in A and B above that the only way you can be sure 500 lbs is transferred to the front axle after all is said and done is by use of a scale. The reason is that I think front end rise measurements become inaccurate and should not be relied on to assume the 500 lbs in fact remains transferred to the front axle. With C) above, the measurement of front end rise is not compromised.
The error in my assumption above that deserves to be mentioned is that in both A) and B) above, I’m stating that you need scales to verify that 500 lbs is transferred to the front axle and in C), I’m assuming the 500 lbs is transferred to the front axle because the front end measurements tell me it is.
While I think about Ron’s reply to my post above, feel free to comment on what I have posted here, just be nice.
