Suspension help

[Ric_Flair]

So I have a 2013 GMC 1 ton doolie pulling a very heavy 44 ft Road Warrior toy hauler.

I added the Firestone air bag system a while back to compensate. Without it, my truck will sit on the overload springs when hooked up.

Everything has worked as designed, except I've blow 2 bags.

So now I'm looking for something better.

Maybe a super spring, but I don't like the idea of a harsher rear end when empty. The truck is also my daily driver.

Maybe a Timbren Load Booster or similar product. Would love to hear feedback from those that use them in similar applications as I have.

Any other ideas you guys might have as well. Thanks

[spoon059]

Yea, that's what it sounds like. I'm guessing that something is close enough that when your bags are filled and weight is on it and they compress just right, it expands just enough to rub or touch something and cause a weak spot.

[Ric_Flair]

Thanks Spoon, will let you know.

Both blow bags were on the passenger side and like you and the others than responded, I'm coming to the same conclusion. There's another variable at play here. Maybe something is rubbing or cutting them. I wish I would have taken a picture before sending them back.

I'll also get under there and see what's going on now as well. Whatever condition that existed then is likely still present.

[spoon059]

Ric... something is wrong. My guess (uneducated at best...) is that when your bags are filled and weight is on them, it stretches the bags out enough that one of the bags is rubbing against something that eventually tears through the bag. Was it the bag on the same side both times?

Firestone airbags are pretty good quality. One failure could be explained away by manufacturing error or some type of road hazard. TWO failures is either an amazing coincidence or else there is something rubbing a back and causing the issue.

If you just decide bags aren't right for you, Timbrens are an option, Roadmaster Active Suspension (RAS) is an option, custom leaf springs, helper coil springs etc are all options for you as well.

Good luck and let us know what you decide!

[Ric_Flair]

Cummins12V98 wrote:
Wes, that's impressive!

I just know I had an onboard in cab pressure gage that I could air up and down each bag. At 5psi unloaded when the RV was added the pressure went to 30psi.

No math formula need for me just visual proof.

That is why I always ask people if the air pressure they are referring to is loaded of unloaded. Still I don't understand why tires are not affected in the same way.

I figured this would be pretty easy to verify so I did.

Aired both bags (new one on passenger side) to 50 psi

Hooked up trailer and measured again. 65 psi

Why don't tires show this dramatic change in static pressure under load? My opinion is because they are bigger and there are 4 (or 6) to spread the weight.

Now, under dynamic road conditions, the 2 bags are taking a lot more force than the 6 tires, plus you have the suspension absorbing some of that as well. That's my layman's take.

I also verified the max PSI for the bags is 100 psi, not 80

[Wes_Tausend]

Cummins12V98 wrote:
Wes, that's impressive!

I just know I had an onboard in cab pressure gage that I could air up and down each bag. At 5psi unloaded when the RV was added the pressure went to 30psi.

No math formula need for me just visual proof.

That is why I always ask people if the air pressure they are referring to is loaded of unloaded. Still I don't understand why tires are not affected in the same way.

Thanks. If, and only if, my reasoning is correct, then your airbags are probably sized less than the bags I described. With less square inches of bag, the pressure would rise dramatically more than my examples.

For the same proportional size reason, tires most likely do rise in pressure when additional load is applied to the vehicle. But there is a lot more square inches of area in a tire to spread the increase around. Each square inch would therefore bear only a small increase, probably not even noticeable if one did pay strict attention to minor differences in the tire guage. One other factor is that a truck guage often squeezes a lot of graduations on the same short ruler in order to measure over 100 pounds when necessary. This means that slight variations in loaded vs non-loaded measurements would not read so obvious.

I suppose one could calculate the actual surface area of a tire. Including some inner steel wheel surface, the tire is merely a cylinder again, but without the end discs. For example, a 3 foot tall tire (diameter) would exceed 9 feet tall were the tire "cut" and the donut-shaped tube "straightened out". In my opinion, that is a big cylinder and it is no wonder that relatively minor pressure increases from added load are not obvious.

Wes
...

[Cummins12V98]

Wes, that's impressive!

I just know I had an onboard in cab pressure gage that I could air up and down each bag. At 5psi unloaded when the RV was added the pressure went to 30psi.

No math formula need for me just visual proof.

That is why I always ask people if the air pressure they are referring to is loaded of unloaded. Still I don't understand why tires are not affected in the same way.

[Wes_Tausend]

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
...

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.

[cummins2014]

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

I ran my airbags a lot with 50 lbs, If I remember my firestone airbags were rated for 100 psi. Also been on some bad roads where I thought the fifth wheel would tear loose, but no issues with the airbags. That is a strange one blowing the airbags.

[Cummins12V98]

"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.

[Dave_H_M]

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.

[Ric_Flair]

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

[Ric_Flair]

Grit dog wrote:
Define very heavy. Either you somehow got 2 defective airbags, not likely cause if they work once they are pretty much good, or you have a stupid heavy pin weight if the dually needs airbags maxed out plus some!
Or are they getting cut by something? You're not specific about what happened.

I've never put it on the scale so I can't say for certain. It's the trailer in my signature and I load it with what I would consider to be the average camping load.

I've sent them back to Firestone. Let's see what they say. I should have taken pictures and posted them but didn't think about it at the time.

[Bedlam]

1. Get Torklift StableLoads to to engage your overload springs sooner and reduce rear end sag.

2. Check air bag pressure when loaded - When hitched, you should be under 100 PSI. Look for obstructions on the underside that may be wearing or piercing your bags. Verify your bag mounts have not shifted creating lateral stresses on the bags as the suspension cycles.

[Wes_Tausend]

mkirsch 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.

Airbags are there to LEVEL the truck, not return it to empty ride height when loaded. Ideally the truck should ride level when loaded on the overload springs.

Dry pin weight is 3225lbs on the 2014 RW415. Even if loading it added 2000lbs to the pin weight you should be well within the payload capacity of a 2013 DRW Chevy.

X-whatever on these two points:

1. That's what the overloads are there for.
2. How much pressure are you putting in the bags?

I always enjoy reading your posts and normally agree with you. But I'm reluctant to believe tire and/or airbag pressures don't increase with added load. I do agree that a pressure increase is often not easily noticable, but it should still be there. If the pressure did not increase with load somewhere along the line, tires and bags would never blow out... they would merely stretch indefinately as you say.

I think it more likely that the pressure only seems to normally stay the same as long as the "rubber" evenly stretches in linear fashion. When the stretch-distortion exceeds a certain elastic design limit (plys), the rubber tears. So extraordinarily compressed air suspension bags will eventually blow out from extreme self-pressure-increase, just as tires will if one just keeps adding weight to a tire already at max recommended pressure. For example this becomes apparent when one might imagine a ridiculous tire overload until the tread face nears (flattens to) the height of the bead on the rim.

Therefore it would be an interesting experiment to closely monitor precise rear tire pressure as one lowers the pin weight onto the truck. I think it should gain at least 1/2 pound or more as a rough guesstimate. The rest of the "squashed" volume should be taken up by innate "stretch-bulge design", maintaining very close to original pressure as you surmised.

For instance, if one were to alternatively lower such increasing weight on a bicyle pump handle, the internal air pressure increase at the pump outlet should entirely appear quazi directly proportional to the added weight because there is little to no stretch in the cylinder walls. Somewhere between a steel pump cylinder and large donut shaped tire, I think the range of small air bags (and small tires) are probably more susceptable to overload pressure blowout due to insufficient, stretchable square wall area.

Wes
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