Air bags and weight distribution--which comes first?

RinconVTR wrote:

Campin LI wrote:

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

"The goal". That's all been made up here and its really pointless to debate and discuss. I want no part of that that because nothing like it ever exists in real life where you have a known weight to transfer with a WDH and that you want to track. It doesn't work that way.

One can measure with a couple passes at truck scale to find out what has been distributed to the trailer and front axle using a WDH, and that discussion ends with actual numbers. Numbers that are nice to know, but you don't "need" to know unless you're checking axle weights in the process.

I understand what you are saying. I am more of a visual person myself. In keeping with the spirit of how this forum functions, explanations are explained in a mathematical format (I just learned that myself). Fictitious numbers have to be used in order to explain how, in this case, a WDH works. Bear in mind that the example refers to a WDH and the fictitious numbers actually refer to percentages of weight so if your weight is actually a little higher or a little lower, the percentage of the weight is transferred the same way. The idea behind a WDH is to distribute the tongue weight across the the axles of the truck and trailer in accordance with guidance (written by engineers) that we accept so that we may obtain a good stable ride. I certainly believe that there is wiggle room within that guidance so that you achieve the ride you are looking to get. The guidance can also change as it recently did.

My issue is that people drive across scales as you suggest to get real numbers when setting up their hitches and they check those numbers against suggested limits and they are right there and think they are good to go. In my experience, like in our houses, we accumulate things as time goes on, so I think that if someone wants to stay under those "numbers", they should not go right up to them on initial setup. If they do not care about those "numbers", then I don't understand why they would bother going over the scale to begin with. Also, if someone sets up their truck right up to the numbers and uses them as a guide for moving items around to be within the "numbers", there is a problem related to fine tuning to obtain a good ride. I think that there is the possibility that someone who sets their truck up and stays under the numbers could have a setup that is not stable and although they think they are doing good, they are not.

BarneyS wrote:
Please try to keep in mind that when someone disagrees with you or posts something different from what you posted, it DOES NOT mean they are attacking you personally or "beating" on you. All it means is that they have a different opinion and have posted what they think.

We all have to be careful to not take our posts too personally. It is my job as moderator to keep personal attacks out of the forum. If someone starts to attack another member, and not just disagreeing with their post, then that post will be gone just as soon as I see it.

We welcome differing opinions. That is what these forums are for, so we can all learn something and help each other out. This thread is a good example of that system at work. :)
Barney

Barney,
I was using exaggeration as an metaphor for expressing thanks.

LOAD TRANSFER GOALS

It should be noted that the OP has a Toyota Land Cruiser. I'm not aware that Toyota specifies any particular WDH adjustment goal for the Land Cruiser.

Campin LI has a Ford Excursion, the last of which was produced in 2005 -- about six years before Ford began to specify that approximately 1/2 of the front end rise should be eliminated via WD.
For the Excursions, Ford specified that the front end should be returned to within 1/2" of its unhitched height.
As far as I know, Ford has not made any of its current WDH adjustment specs retroactive to vehicles made prior to 2011.

Ron

Campin LI wrote:
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.

For the example scenario -- if application of WD caused 500# to be added to the front axle giving -500+500 = 0 net load change, then 750# would be removed from the rear axle giving +1500-750 = +750# net load change. IMO, adding 750# to the rear axle would not cause an unstable ride. Most vehicles, especially trucks, are designed to handle this.

If the goal is to restore both front and rear to the unhitched heights, that can be accomplished by trial and error -- using the air bags to help lift the rear while using the WDH adjustments to return the front to its unhitched height.
If you get lucky and add the right amount of air pressure (lifting the rear part of the way to its desired height), adding WD will cause the front to drop to its desired height while causing the rear to rise to its desired height.
By adjusting the WDH last, the final adjustment is to the front end load (height) rather than the rear end height.
Since there are no manufacturer specs for rear end height, it's better to get the front end as close as possible to spec.

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.

Does "level stance" mean the rear end, when unhitched, is higher than the front? If so, some vehicles take on close to level stance just by adjusting the WDH to return the front end to its unhitched height.
If you need to use the air bags for additional lift, you can use the same procedure as A) to get both front and rear to their desired heights.

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.

And, as in A) or B), you could slightly overload the front axle with the WDH and then add enough pressure to bring the front end load (height) back to the desired value. In the process, you would gain some additional "stiffening" of the rear suspension.

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.

Bouncing the front and rear up and down a few times before measuring the heights might help to reduce some of the errors.

Ron

Campin LI wrote:

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.

Yes, heights should be measure at the wheel well opening -- along a vertical extending from the pavement, past the center of the wheel cover, and up to the fender. The axle serves as the pivot (fulcrum). Measuring directly in line with the axle eliminates any effect of chassis pitch-axis rotation.

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.

Sorry about that. The "coefficients" are spring coefficients with units of pounds per inch. A coefficient of 500 lb/inch means an added load of 500# will cause the suspension to compress by 1 inch.

"Yaw" is rotation about a vertical axis.

Ron

Please try to keep in mind that when someone disagrees with you or posts something different from what you posted, it DOES NOT mean they are attacking you personally or "beating" on you. All it means is that they have a different opinion and have posted what they think.

We all have to be careful to not take our posts too personally. It is my job as moderator to keep personal attacks out of the forum. If someone starts to attack another member, and not just disagreeing with their post, then that post will be gone just as soon as I see it.

We welcome differing opinions. That is what these forums are for, so we can all learn something and help each other out. This thread is a good example of that system at work. :)
Barney

Campin LI wrote:

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

"The goal". That's all been made up here and its really pointless to debate and discuss. I want no part of that that because nothing like it ever exists in real life where you have a known weight to transfer with a WDH and that you want to track. It doesn't work that way.

One can measure with a couple passes at truck scale to find out what has been distributed to the trailer and front axle using a WDH, and that discussion ends with actual numbers. Numbers that are nice to know, but you don't "need" to know unless you're checking axle weights in the process.

I don't know if I'd call it a beating, as much as a "gentle nudge" toward the mode of thinking you needed to employ. We are all here to learn - there isn't a time that I come on here that I don't learn something new.

;-)

Campin LI wrote:
Although not specifically relative to the question, let me explain my real world experience. I tow a trailer with 1200 lb tongue weight with my Ford Excursion. With the kids in the truck, it is weighed down pretty good. When on rough road or bumpy road, the back of the truck could feel a little floaty so I decided to add airbags. The WDH has always been adjusted with the front slightly high because when I set the hitch up, I felt it drove better this way. (It is only a coincidence that the new way was recommending this and was published later). When I put air in the airbags, I raised it until the truck was more level when hitched up, I'm guessing about an inch or 2. I did not notice much front end rise but in the end it did rise a little (I posted a question here a while back and I just looked it up and it turns out you are the one that assured me that it did rise). Anyway, it drove terrible. I adjusted the hitch many different ways and in the end I dropped the air pressure down to a point where I just saw the rear of the truck rise and my ride has become quite comfortable. The back of the truck is real stable and that floaty feeling is gone. My WDH adjustment is exactly what I used before the airbags were added. To me, the addition of the airbags was a success in that I achieved what I wanted, but the OP wants a level stance so I suggested a different approach which you somewhat agreed would be appropriate.

Not that my setup problem was the same as the OP's but I'm glad I posted. Even though I got ripped for what I wrote and came back for more of a beating, overall, my interest in the thread was also self serving. All this thinking has made me realize that I made 2 errors due to over thinking what I wanted to do when I added airbags to my truck. My biggest problem was taking measurements from the bumper because when they didn't make sense I started rationalizing why and made my second mistake by concluding that the front of my truck should rise to maintain the rake. I was too stuck trying to relate the problem with the rise in rear height and it never dawned on me that the point of support changed the rake. God only knows what I was doing to my weight distribution which made my ride so bad. Frustrated over nothing. But I feel relieved.

I hope after all this the OP knows what he needs to do.

RinconVTR wrote:

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.

Your last sentence in this quote is exactly what I'm talking about. You threw a blanket statement out there, and now you've modded your statement with an if/then statement. You didn't have that in the initial statement. I wanted you to see that such a blanket statement doesn't work.

There is no "rear sag to spec" in WDH setup. You set the hitch up to transfer weight back to the front axle and TT axles. Rear sag does typically change when you do so, but you aren't adjusting your setup to achieve a specific sag in the rear. As mentioned above, you target 1/2 the difference of unloaded front height, and loaded front height for your WDH, and the rear goes where it goes. This is how Ford specs WDH setup currently, and I believe that is the case with Chevy and Dodge as well. It might go back up an inch, it might move 1/16" of an inch. What the back does is Irrelevant. The front height is what you are working toward.