Air Bags - What Do They Do?

[TDF5G]

To JIM W yes that helps to understand it better. thank you

I think you're right, but if you were to raise the rear of a vehicle past level then I would think that would put some weight on the front wheels (and some to the trailer), not a considerable amount but some weight.

I too thought about race cars a few days ago as JAY D did. Crews make many adjusments to suspension components to move weight around and improve handling, a race car has to weigh a certain amount, but that's another discussion.

After thinking this over and doing some experiments I might not be taking in to consideration the hitch weight of a trailer possibly, I must be thinking about a vehicle with no trailer. I do understand the way a WDH hitch works. It's just the air bag thing I'm still working on.

I'm not really agreeing or disagreeing with anyone here, I'm only trying to understand it. Just because someone states something does not make it true. So I'm doing my own research.

Thanks to all the replies, this is interesting. I'm sorry to get away from the original post here. I don't believe an air bag increases the GVWR or GAWR of any vehicle. I do believe an air bag helps spring rate (compression) but not load capacity. I'm just curious about the weight distribution.

[christopherglenn]

Adding air to airbags in the rear suspension will raise the rear of the truck (duh), and if not towing, thats about it. With a trailer attached in the bed (5er / GN) you get about the same result. With a trailer attached to the bumper / reciever hitch the weight is well behind the axle, and raising the rear axle will do little to nothing to the front axle - unless you have WD attached. Raising the rear with WD attached will unload the wd (as noted on page one, air up and the WD goes slack). A similar effect happens crossing anything that raises the rear axle above (an imaginary line between the front and trailer axles). Think a speedbump, or cresting a hill with either the front or trailer below the other axles. When this happens the front axle unloads (the weight is behind the rear axle, and without working DW it is no longer shifted off the rear axle), as well as shifting back the weight that the WD transfered to the trailer axle. The WD acts like a spring (it is a spring, or two) allowing it to streighten out unloads it.

[TDF5G]

Yes I see what you're saying. I do understand the WDH as I said before.

But now I'm thinking of gravity. If you parked a truck and trailer on a hill, say going down hill, wouldn't there be more weight on the front axle than the rear? And vice versa if going uphill. The rear would be higher that the front. I'm not talking about a tremendous amount of weight but a few pounds would transfer from one axle to the other wouldnt it? Just due to gravity.
I think it would be like two guys lifting a log, the lower end would be heavier.

[happytrails]

I have air bags and I didn't put them on to try and get within my payload that I am very likely exceeding. I keep about 40PSI in them when hauling. In reading about WDH I know/read that some of the tongue weight (which adds to payload) is shifted back to the trailer and from what I read it is around 30-33%. I don't know if that is accurate, it's just what I have read. From what I understand if I have a tongue weight of 1000# then about 300# is transferred back to the trailer thus leaving me with only 700# as payload. If what I have read is wrong please let me know and give me a good source where I can read up on it.

Once I added the air bags I DID have to adjust my WDH. What the air bags did for me, and what I wanted them to do, is take out some of the bounce. I travel a lot of back roads that have a lot of swells and dips and the truck was bouncing A LOT. Someone recommended air bags so I got them and they were right; not nearly as much bounce.

If by some crazy miracle they did actually move some of the tongue weight back to the trailer it probably didn't make a difference because I still have to use a WDH to finish the job. The other part of the WDH for me is SWAY CONTROL!! Even if the air bags could completely do the job of the WDH you still have to have some sway control don't you? My WDH has provided me with fantastic sway control as I have not noticed any sway even when trucks pass me up.

All I can say is my combination works well for me and so far I feel VERY comfortable that I can easily maintain fantastic control of my rig under normal and some stressful driving conditions. Oh and a great feature that I had only read about in my truck manual (until last weekend) that is on my Tundra is that it has it's own sway control and IT WORKS VERY WELL! (real bad road condition) When it went off it sounded like anti-lock brakes which is essentially what it's doing but just applying braking to different wheels to get the back end straight again. Keeps the tail from wagging the dog. Thank you Toyota, you probably saved my truck and trailer from running off the road.

[scrnt]

for those of you that have air bags what on compressor do you use? what size i am looking at the air lift 5000 bags.

[rnkburg]

I had there compressor on a previous vehicle, it didn't last very long. I did like the gauges and controls in the cab though. This round I am not using a mounted compressor just fill/ check when I need to. Plus i ran out of mounting room under hood

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[happytrails]

I don't have on board compressor. We camp quite a bit so I leave mine at 40 and I use some of those caps you can get at auto parts stores that have different gauge level numbers and will be green if good or red if bad. I just check to make sure they are ok before I leave. One thing I can tell you is that when I was constantly checking my bags I was somehow loosening the needles to a point where they started leaking. It took me a little bit to figure out where the leaks were but now that I know I keep a needle tool in my truck and some spare needles. The gauge caps I bought also keep a good seal on them so they are less likely to leak too.

[Jim W]

Originally Posted by Jay D

I would think that some weight would move!!!! I work on a race car and with the car on the scales when ever you turn any of the 4 springs up or down (raise or lower the chassis) you could see on the scale the #'s (weight ) being moved to the opposite side. LF - RR and RF - LR or both rears would move weight to both fronts and same would go for the fronts. Does that make sense to all. Jay

Jay

With a race car they are designed to support so much weight on each corner (tire and wheel along with the suspension components) correct? Now each corner is supported by a coil spring attached to some component at that corner. When you adjust the spring to collapse it or extend the spring you are changing the load that this spring will support( spring rate) in so doing you are transferring the remaining weight to the other corners to be support.

With air bags these are not collapsing or extending the leaf springs on the truck. Therefore they are not changing the spring rate so the load they support (leaf spring) has not been transferred to another part of the truck. They are just supplementing the added force to carry this load on the leaf springs.
Jim W.

[Jim W]

Originally Posted by scrnt

for those of you that have air bags what on compressor do you use? what size i am looking at the air lift 5000 bags.

I bought the system that Air Lift offers the Air Lift Sure Set system No. 25004. The compressor is mounted on the inside rails of the frame by the transmission. In this way the Air tubing runs are not too long. The kit includes the compressor, tubing, controller with gages, manifold with transducer and all of the wiring for the install.
Jim W.

[christopherglenn]

If you are going to manually fill the bags, any compressor that will hit 80-100 psi will work. The higher the psi rating, the less air it pumps per cycle of the piston. In a pinch you could inflate with a bicycle pump.

I will give you that a SLIGHT ammount of weight can be shifted to the front axle (due to gravity) by lifting the rear. Attach the trailer (no wd) with the airbags empty, put detail tape vertical above the centerline of the rear axle. Inflate the airbags to where you want it, and put a second piece of tape vertical above the rear axle. The wedge between the pieces of tape would be moved from behind the rear axle, to in front of the rear axle. The huge distance between the axles, a few percent of the weight of the wedge actualy shifted from axle to axle. As far as weight shifted on the trailer, same deal, raising the tounge / pin 4 inches - 20 feet in front of the axles - with 10 feet of trailer above the axles, you would shift 2 inches of roof from behind the axles to in front of the axles. Unless there is an AC there, there isn't much weight to move, and 20 feet from the tounge / pin you would see an even smaller percentage change up front.
Once you put WD on the effect from gravity is unimportant, a few lbs shift from gravity VS hundreds of lbs from the springs in the WD.

[rhagfo]

Originally Posted by Jay D

I would think that some weight would move!!!! I work on a race car and with the car on the scales when ever you turn any of the 4 springs up or down (raise or lower the chassis) you could see on the scale the #'s (weight ) being moved to the opposite side. LF - RR and RF - LR or both rears would move weight to both fronts and same would go for the fronts. Does that make sense to all. Jay

Originally Posted by rhagfo

If you are only changing one corner, then you will move weight as the diagonal wheels act as a pivot point, but if you raise both on either the same end or side you will not likely see any weight movement, unless you raise it several feet.

Let me clarify the above statement.

1. To all those that believe that lifting the rear will transfer weight to the front, for the discussion here no! I absolute measurement yes, but the amount in the amoutn of lift we are discussing would likely be less than 5# on an 8,000# truck.

2. To the statement of weight jacking a race car 100% true, but only because corner to corner you now have a pivot point involved.

Say you add two turns on a spring on the right rear of a race car the left front will see increased weight, because you have created a pivot between the left rear and right front!

If you lift both rear corners the same the pivot point is now between the two front wheels, so there is no weight added to the front axle, we are talking inches not feet here.
Now if you lifted the rear of the truck say three feet, then weight would start to show up on the front axle.