Hypothetical SUV towing travel trailer with 1200 lb tongue weightQuestion / clarification:Without weight distribution hitch - back of truck goes down and front of truck goes up.With weight distribution hitch - back goes up a little, front goes down a little.No weight distribution hitch - pump up air bags to bring back of truck up to unhitched height. Front of truck is not high. Why is this. The same weight is pushing down at the hitch. I would think the front of the truck would still rise because no weight is being transferred to the front of the truck.Thanks for your ideas / opinions.

Basically, the weight distribution hitch transfers weight across the whole vehicle. Acts as a leverage point to send some of the tongue weight towards the front of the vehicle. Not affected by airbags since the hitch is attached to the frame. The airbags push down on the rear axle to raise the rear of the SUV up.

the bear II wrote:The airbags push down on the rear axle to raise the rear of the SUV up.I follow you but I see this a little different. The weight pushing down on the rear axle is the same with or without airbags, therefore, I think of it as the airbags pushing up on the frame to lift the rear of the truck up higher. Probably the same as what you are saying though (is the glass half full or half empty type thing).There is no effect on the weight that was lost off the front of the truck. The front should still go up.... but it does not.I'm wondering if most of the front end rise on the truck without weight distribution and without air bags is actually due to the rear drop when the weight is added to the hitch and not so much related to the weight lost from the front axle (dynamics of suspension, etc). After all, with a 1200 lb hitch weight, only about 200 lbs or so is removed from the front. It is almost equivalent to having a passenger in the truck or not. Maybe the suspension automatically absorbs that type loss? Just thinking out loud.

Don't forget that some of weight is also moved to the front axle of Trailer

ReferDog wrote:Don't forget that some of weight is also moved to the front axle of TrailerAgreed, I'm not trying to say a weight distribution hitch is not needed. I fully understand the benefit of having one.To come clean, I added airbags to my SUV to try and stiffen a bouncy ride when towing. When I pumped up the air bags, it unloaded my spring bars. I ended up airing down the bags quite a bit where the rear of my truck was low but not as low as without. The ride was a lot better with no bouncing and overall it was a good addition to my setup but the back end of my truck is still down a little now. I also tried tilting the hitch head down another washer and then engaging the WDH and then airing up the bags to unhitched height, but then the front went down lower than the other way with no airbags. Sorry no scaled weights. Everything I did is based on measurements and eyeball. By the way, it is a 2005 Excursion towing a Jayco 32bhds.

You might try adding air to the air bags and then hook up the trailer, then adjust the rear height with the WDH bar tension. But you need to make sure you don't take too much weight off of the rear suspension to provide good traction.Even my medium duty truck with a full air ride rear suspension that automatically adjusts for loads, sinks a little (about 3 inches)when I put the weight of the trailer on it.Keep playing with the tension bar adjustment until you get the ride you want and then be happy with a little sag if it's there. If you pay attention to the TTs going down the road, nearly half have a tow vehicle with rear end sag even with a WDH.

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babies_dadeo
Explorer
Aug 09, 2013
Long and short of it is that most front end rise due to hitch weight is related to the suspension, not the loss of weight from front axle due to the load behind the rear axle.

Makes me think that as far as a weight distribution hitch goes, it's really the act of raising the back of the truck that makes the difference in ride stability rather than the transfer of weight to the front.

Adding the airbags did not make or break my setup but I did notice that there is a lot less bounce in the back when I hit those type roads that have those wavy surfaces. More than likely, my WDH is doing less work now too.

Bingo!

Just my opinion, but with todays HD suspensions, the truck is built to handle so much more weight then they once were it makes judging vehicle angle and WD a much different process. I do know that with Heavy trucks, (Semis), weight movement is never an exact science, as you move a 5th wheel, sure you should move X kg from this axel to this axel, but it does not always work that way because of the dynamic nature of the units weight, length and suspension (hugely exaggerated due to air suspension). From what I am hearing you actually have a solid setup and the airbags are doing exactly what they are supposed to.
Happy Camping!
Campin_LI
Explorer
Aug 08, 2013
Ron Gratz wrote:
Campin LI wrote:
So what causes the front to drop when air bags are pumped up?
The front should not drop.

If you can provide some actual before and after height measurements, I will try to interpret the numbers.

Axle load data would be even better.

Ron
Your right! I re-hooked up and it is more an illusion that the front went down. The truck bumper rolls slightly toward the road and the wheel well rotates slightly therefore giving an illusion that it goes down. After reading other posts on airbags, Although it rode real well last time I used it, I'm going to raise my hitch head back to where it was and only put enough air in the bags to see the rear of the truck start to rise. I will then decide which ride is better. Thanks for your help on this.
Ron_Gratz
Explorer
Aug 04, 2013
Campin LI wrote:
So what causes the front to drop when air bags are pumped up?
The front should not drop.

If you can provide some actual before and after height measurements, I will try to interpret the numbers.

Axle load data would be even better.

Ron
Campin_LI
Explorer
Aug 04, 2013
Ron Gratz wrote:
Campin LI wrote:
When WDH is engaged, front is higher than unhitched by about an inch and back is down by about 2 inches. When air bags are pumped up to get the rear back up to unhitched height, the front does not go down to unhitched height, it is still a little high.---
When you use the bags to lift the rear of the TV, you also are lifting the hitch and the trailer tongue. This changes the vertical angle between TV and TT which has the same effect as tilting the ball mount forward. The load on the WD bars will be reduced, and the amount of load transfer will be reduced.

Reducing the load transfer will cause load to be removed from the TV's front axle. The front of the TV will tend to rise.
Whether the front actually will rise depends on the amount of friction in the front suspension components. The front might not rise, but you should not expect it to drop.

On edit: To be more specific, No WDH - hook up trailer. Front is way up (not sure how high, maybe 3 inches?)and back is down. Pump up airbags and as back goes up, front goes down. This happening is what I don't get.
Does your TT have independent axles or does it have an "equalizer" link between the front and rear springs?

If you really want to understand what is happening to the front end you'll need to measure the axle loads under the various conditions. Height measurements often are not a reliable indicator of loading.

Ron
The trailer has an equalizer link between the 2 axles.

I realize scale numbers would explain a lot. When I posted the question, I kind of thought there would be 20 replies with the same answer. I'm actually surprised there is no overall consensus on this.

I have to believe the suspension has a lot to do with it. Or the WDH actually equally distributes the load across the entire TV chassis and the angle the truck makes with the road surface has something to do with it, ie by raising the back with airbags more load goes to the front axle because the truck is level. Not sure.
Campin_LI
Explorer
Aug 04, 2013
Ron Gratz wrote:
transamz9 wrote:
---The natural arch in the leaf spring is flattened out when the load is applied so the front of the leaf spring is naturally going to lift the front of the SUV.---
Yes, if a downward force is applied to the hitch, there will be an increase in the upward force on the frame at the rear spring's front mounting point. And, if we assume the chassis is pivoting about the rear axle, the increase in upward force at the front mounting point will tend to cause the front of the TV to lift.

However, there also will be an increase in the upward force on the frame at the rear spring's rear mounting point. And, that upward force will tend to cause the front of the TV to drop. The net effect on the front end of the TV will be essentially zero.

The downward force on the ball will cause the load on the TV's front axle to be reduced, and that is what causes the front of the TV to rise.

Now when you add air to the bags, the weight on the truck is not changing but you are relieving pressure from the leaf spring allowwing the spring to relax also allowing the weight the spring was taking off of the front axle to return to the front axle.
Yes, you now are relieving load from the rear leaf spring. But, you must keep in mind the loads will be reduced on both the spring attachment point in front of the rear axle and the attachment point behind the rear axle. Again, the net effect on the front axle will be essentially zero.

Ron
So what causes the front to drop when air bags are pumped up?
Ron_Gratz
Explorer
Aug 03, 2013
Campin LI wrote:
When WDH is engaged, front is higher than unhitched by about an inch and back is down by about 2 inches. When air bags are pumped up to get the rear back up to unhitched height, the front does not go down to unhitched height, it is still a little high.---
When you use the bags to lift the rear of the TV, you also are lifting the hitch and the trailer tongue. This changes the vertical angle between TV and TT which has the same effect as tilting the ball mount forward. The load on the WD bars will be reduced, and the amount of load transfer will be reduced.

Reducing the load transfer will cause load to be removed from the TV's front axle. The front of the TV will tend to rise.
Whether the front actually will rise depends on the amount of friction in the front suspension components. The front might not rise, but you should not expect it to drop.

On edit: To be more specific, No WDH - hook up trailer. Front is way up (not sure how high, maybe 3 inches?)and back is down. Pump up airbags and as back goes up, front goes down. This happening is what I don't get.
Does your TT have independent axles or does it have an "equalizer" link between the front and rear springs?

If you really want to understand what is happening to the front end you'll need to measure the axle loads under the various conditions. Height measurements often are not a reliable indicator of loading.

Ron
Ron_Gratz
Explorer
Aug 03, 2013
transamz9 wrote:
---The natural arch in the leaf spring is flattened out when the load is applied so the front of the leaf spring is naturally going to lift the front of the SUV.---
Yes, if a downward force is applied to the hitch, there will be an increase in the upward force on the frame at the rear spring's front mounting point. And, if we assume the chassis is pivoting about the rear axle, the increase in upward force at the front mounting point will tend to cause the front of the TV to lift.

However, there also will be an increase in the upward force on the frame at the rear spring's rear mounting point. And, that upward force will tend to cause the front of the TV to drop. The net effect on the front end of the TV will be essentially zero.

The downward force on the ball will cause the load on the TV's front axle to be reduced, and that is what causes the front of the TV to rise.

Now when you add air to the bags, the weight on the truck is not changing but you are relieving pressure from the leaf spring allowwing the spring to relax also allowing the weight the spring was taking off of the front axle to return to the front axle.
Yes, you now are relieving load from the rear leaf spring. But, you must keep in mind the loads will be reduced on both the spring attachment point in front of the rear axle and the attachment point behind the rear axle. Again, the net effect on the front axle will be essentially zero.

Ron
transamz9
Explorer
Aug 02, 2013
With the air bags or not the tt is still going to remove weight from the front. If you don't want to weigh the rig then I would get a measurement from the ground to the top center of the front wheel well when the SUV is unloaded and then return it back to that measurement once the tt is hooked and you get your bags at the pressure you want using the WD system.
Campin_LI
Explorer
Aug 02, 2013
transamz9 wrote:
If your tongue weight is 1200# then that will be between 300 and 360# your tt is taking off of your front axle not counting for the rear suspension taking weight off also. If I knew your actual measurements I could get that number closer to exact.
I don't have the measurements of the truck off hand. I realize that weight was removed by the hitch which is why I use the WDH. It was the change in front end height that had me stumped.

With the airbags, when I tilted the hitch head back a washer, once engaged the front was lower than before the airbags were installed, so I knew that was too much tilt and went back to the original tilt. It's good to know that there is a good amount of leeway in the adjustment as our trailer is always loaded differently and so is the truck for each trip.
transamz9
Explorer
Aug 02, 2013
If your tongue weight is 1200# then that will be between 300 and 360# your tt is taking off of your front axle not counting for the rear suspension taking weight off also. If I knew your actual measurements I could get that number closer to exact.

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