Air bags and weight distribution--which comes first?

RinconVTR wrote:
I just mentioned previously, Option B is telling me the WDH isn't set up very well if this example requires air in the bags to level out the TV after the WDH is set.

I understand what you are saying but if you have reached the goal of 500 lbs restored to the front axle, the back is wherever it is. If you distribute more weight to the front to raise the back, you will be transferring additional weight to the front axle exceeding the 500 lb goal. You will get the truck level but you will remove more than the goal amount from the rear axle to accomplish that.

On edit: I screwed up the quote and I don't know how to fix it

Ron Gratz wrote:
I don't know of any theory which says the front of the truck should rise when you add pressure to the bags without WD being applied. But, it would be easy to test experimentally. Just measure the following:
1) Front and rear heights for truck only with no pressure in the bags and trailer not hitched.
2) Front and rear heights for truck with trailer hitched and no pressure in bags.
3) Front and rear heights for truck with trailer hitched and pressure in bags.

Me either, I am making an assumption that if you raise the back of the truck 2", because the loading on the truck does not change, the front should theoretically raise by the same 2". My thought process is that the airbags pumped up are moving a horizontal datum (of the truck) up 2" vertically (The rake of the truck must remain the same with air in or out of the airbags). I know on my truck, this did not actually happen, I'm thinking maybe suspension friction? Not sure though. The fact that it didn't rise 2" is what makes me think front end rise measurements have been compromised and therefore cannot be relied upon.

Second thoughts popping into my brain now are that the support of the load is what has changed and height does not really come into play because the front of the truck just rotates over the axle.

I think it's starting to make sense. Sorry for thinking out loud.

******Now I don't think there is any front end rise that's going to take place at all. Using a measurement for front end rise directly over the front axle or at wheel well would solve the issue of measurement inaccuracies due to the change in rake of the truck after air is in the airbags.

If agreed, I think my post above could be simplified quite a bit by combining A) and B) above by taking front end measurements directly above the front axle or at the wheel wells to correct for change in rake (don't use bumper measurements). A) and B) from my post above can be accomplished with a little trial and error by adding or removing air and adjusting the WDH each time to maintain appropriate front end measurements.



You mention coefficients above and give them numbers when you set the scenario. What do they represent? Also, if you don't mind, what does "yaw" mean. I tried to look it up but I still don't get it.

Thanks.

On edit: Edited for clarity but I tried to leave the original post somewhat in tact.

Campin LI wrote:
Here is my take.


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.

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.

.

I agree with your B and C except as I just mentioned previously, Option B is telling me the WDH isn't set up very well if this example requires air in the bags to level out the TV after the WDH is set.

93Cobra2771 wrote:

RinconVTR wrote:
Not two different objectives. Not at all.

Set up the WDH first. This implies doing so correctly. If there is too much rear sag, that means the WDH isn't set up correctly.

K.I.S.S. Keep it simple stupid.

I have to disagree with this statement. Every combination is different - some truck springs are softer in the rear than others. To throw a blanket statement out there there saying too much sag means the WDH isn't set up correctly doesn't work.

.

It sure does. WDH works with soft springs and hard alike. You wont find anything in text to back up what you're saying because it contradicts what WDH is designed to do.

That said, soft sprung trucks and SUV's may see a reduction in ride height at the front in order to get the rear sag in spec, contrary to book specs. But WDH will absolutely correct rear end sag when set up correctly. Again, that is what its designed to do.

If you have too much rear sag with a WDH and adjustments don't appear to change anything, then your weights are higher than what you thought and/or you have the wrong class WDH to handle the weight.

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.

RinconVTR wrote:
Not two different objectives. Not at all.

Set up the WDH first. This implies doing so correctly. If there is too much rear sag, that means the WDH isn't set up correctly.

K.I.S.S. Keep it simple stupid.

I have to disagree with this statement. Every combination is different - some truck springs are softer in the rear than others. To throw a blanket statement out there there saying too much sag means the WDH isn't set up correctly doesn't work.

The simple fact is this: If you change the rear ride height ANY AT ALL with air bags, it WILL affect the WDH setup. To say otherwise is quite simply wrong, and my earlier example (with real world numbers) is proof of that. ANY change in rear ride height WILL change the angle between the TV and the TT, and thusly, the amount of weight being transferred. Setting up the WDH first in this scenario will result in changes once the bags are aired up. I got lucky, as I was planning on adjusting my WDH to tranfer LESS weight to the front. Raising the rear up without any other WDH change made the "adjustment" for me. I blundered into my ultimate goal with luck - and didn't have to make any actual adjustments after my airbag installation. If I hadn't gotten lucky, I would have gone through the initial WDH adjustment procedure and probably added a washer to increase weight transfer.

If the rear ride height isn't changed with addition of air to the bags, then setting the WDH up either before or after the addition of air doesn't matter. Why? Because the ride height in the rear hasn't changed. In this setup, the bags are being used more like an overload leaf in the spring pack. So setting up before or after air is in the bags doesn't matter, in this case.

Not two different objectives. Not at all.

Set up the WDH first. This implies doing so correctly. If there is too much rear sag, that means the WDH isn't set up correctly.

K.I.S.S. Keep it simple stupid.

RinconVTR wrote:
We've debated this before, and while your logic is sane, it is not reality in most cases. You can in fact add air without inducing lift.

WDH should ALWAYS be set up BEFORE adding air.

Now, depending on the bags, depends how much air you can add before you get lift. Poly bags allow a lot more air, while adding spring rate, and not lift. Rubber bags, like many trucks have installed, don't take much air before lift occurs.

Either way, the point is to increase spring rate and not induce lift.

I don't think there's been any disagreement about whether you can add air without inducing lift.
Obviously, you can -- it's just a matter of how much pressure can be added before lift begins.

However, that has nothing to do with what the OP wants to achieve.
He has a TV which experiences significant squat, and he wants to eliminate some or all of the squat while getting a proper amount of load transfer.
IOW, he wants to induce a considerable amount of lift.

In your case, you just want the bags to "stiffen" the rear suspension without inducing any lift.
That's not what the OP wants to do.

The OP's objective and your objective require two different approaches.

Ron

Here's a link I saved from the last time we went around this same topic:

http://www.etrailer.com/question-9425.html

Edit: And another.

http://www.etrailer.com/question-45926.html

Ron Gratz wrote:

Damdifino wrote:
---My question is, what do I do when hitching up? Air up the bags first, then weight distribution? Vice-versa? How do I go about integrating the air bags with the weight distribution hardware?

AlbertaNewbie got it right -- air up first, then add tongue weight, then add wdh.

I don't know why Equal-I-zer would say to attach trailer and wd to tv first, then air up. There's nothing to that effect stated in their online set up instructions.

When you adjust the WDH first, and then add air, the bags will lift the rear of the TV.
When the bags lift the rear of the TV, the load on the WD bars will decrease.
When the load on the WD bars decreases, the load on the TV's front axle will decrease and the load on the rear axle will increase.
When the load on the front decreases and the load on the rear increases, the WDH will no longer be properly adjusted.
When the WDH is no longer properly adjusted, you get angry.
When you get angry --- (sorry, I just watched a DirecTV commercial)

Ron

We've debated this before, and while your logic is sane, it is not reality in most cases. You can in fact add air without inducing lift.

WDH should ALWAYS be set up BEFORE adding air.

Now, depending on the bags, depends how much air you can add before you get lift. Poly bags allow a lot more air, while adding spring rate, and not lift. Rubber bags, like many trucks have installed, don't take much air before lift occurs.

Either way, the point is to increase spring rate and not induce lift.