Air Bags

[Campin_LI]

Hypothetical SUV towing travel trailer with 1200 lb tongue weight

Question / 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.

[SteveAE]

Using a weight distribution hitch, take your rig to a scale and put only your front wheels on the scale. When you add air to the air bags you will see the weight come off the front wheels. The change isn't huge, but it is there.

[Campin_LI]

93Cobra2771 wrote:
Adding air to the bags is throwing off your original setup due to the increased angle between the TV and the TT.

The added air will cause the WDH to transfer less weight to the front and TT axles.

You need to scale it and get your hitch adjustments made. Then all will be good.

If not scaling it, it is somewhat of a guessing game, especially with heavier truck suspensions.

Understood. I knew that going into it. I've got it dialed in good and it tows well. I tried to be vague in the first post because I didn't want people to think I was having trouble setting it up.

My question really relates to front end rise and why it does not exist when I pump the airbags up to achieve unhitched height when weight distribution is not engaged. Because no weight is transferred to the front (without WDH), the front should still rise (theoretically?) when I hitch it up.

[93Cobra2771]

Adding air to the bags is throwing off your original setup due to the increased angle between the TV and the TT.

The added air will cause the WDH to transfer less weight to the front and TT axles.

You need to scale it and get your hitch adjustments made. Then all will be good.

If not scaling it, it is somewhat of a guessing game, especially with heavier truck suspensions.

[Campin_LI]

the bear II wrote:
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.

Funny, we are thinking along the same lines. I just edited the post above to explain that I did exactly what you suggest here. I am happy with the ride and the back is not really down that low.

I am really just wondering why the front end of the truck behaves as it does with the airbags. Probably thinking too deep. Excursions have 44 gallon fuel tank which is located behind the rear axle. Full or empty (300 lb plus or minus difference) there is no change in ride height that I can tell.

[the_bear_II]

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.

[Campin_LI]

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

Agreed, 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.

[ReferDog]

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

[Campin_LI]

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.

[the_bear_II]

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.