Suspension help

Ric Flair wrote:

up2nogood wrote:

Ric Flair wrote:
To answer some of your questions.

Sitting on the overloads in a static state is not the problem, however, with the dynamics of varying road conditions, and without some help (bag, supersprings, etc) I frequently bottom out.

I fill to ~50-60 PSI. Why I have blow 2 bags is a mystery to me. Both times have been on long trips, some of it over some bad roads.

50-60 before hitching up ???

After, and that's what it takes to level out the truck to my calibrated eye.

If I recall, they are rated to 80 psi

The pressure might exceed the 80 pounds, even if it starts at a lower setting (60 psi), according to the next two posters and theory. I didn't fully realise this myself until Mathew (MKirsch) made me think more about it in an earlier post.

Resulting bag air pressure after pin loading could actually be calculated by dividing the pin weight by the number of real square inches that a pair of roundish suspension bags have in the interior surface of their quazi-sphere, or cylinder, shape.

As an example, suppose the pin weight is 3000 pounds. If the airbags are 8 inches and spherical, the formula is..., and I calculate the surface area would be 4pir², or 4 times 3.14 times 4x4 (=16, radius squared).

I think a single bag surface area would then be roughly equal to 201 square inches. Since there are two bags, each would only support 1500 pounds of the 3000 pound pin when parked, so 1500 lbs divided by 201 sq in equals around seven and one half pounds per square inch of static pressure increase.

However driving might hit an occasional nasty bump that, by inertia, momentarily raises pressure at 3g's, resulting in 9000 pounds of effective pin weight, and a 22.5 pound pressure increase. If the bags were already inflated to 60 psi, they would peak at 82.5 psi which would be a slight over pressure. This would be close to bounds providing the bags are not even smaller.

As another example, suppose the bags were cylinder shaped and measured a generous 8 inches high by 6 inches diameter. Since the ends of the cylinder are closed, we must calculate the both the area of the "wrap" and the circle discs at the ends. The formula for this is A = pid(r + h), where pi is 3.14, diameter(d) is 6, radius(r) is 3 and height(h) is 8.

I calculate the area of this cylinder-shaped airbag to be 207.24 sq in. This marginally larger area is only a slight improvement to the 201 sq in of the earlier spherical bag mentioned above. Since Mathew is absolutely correct that tires and bags do deform under pressure, the actual shape of a real inflated bag would probably be somewhere between a sphere and cylinder. And we do not know the exact size of Ric Flair's bags, so the calculations would certainly change, but we should be close.

I was never a great mathematician, and I'm pretty old and rusty, so the accuracy of the conclusion is open to debate, and I invite anyone to doublecheck my calculations and reasoning.

Wes
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Dave H M wrote:
Just like a tire, adding weight does not increase the pressure in the bags. The bags simply change shape. They bulge out as the suspension is compressed. He is overinflating them in the first place.

:h So is that a fact on your truck?

Not so on mine, there is a very noticeable increase in pressure when the load/fifth wheel is dropped down on the hitch.

Cummins12V98 wrote:
"Just like a tire, adding weight does not increase the pressure in the bags. The bags simply change shape"

No disrespect you are completely wrong! I had bags on my 11 RAM. I ran them at 5psi unloaded. Once the 4-5K pin weight was added the pressure in the bags went to 30psi.