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 > Let's talk air bags...

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Geewizard

WA

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Joined: 08/25/2004

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Posted: 01/16/22 09:01am Link  |  Quote  |  Print  |  Notify Moderator

I run 5 PSI unloaded and 70 PSI with the camper on. The camper weighs about 2200 Lbs all up. No bouncing unloaded and of course no bouncing loaded. No overload springs, just stock leaf springs in the rear. Wouldn't be without the airbags.


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ajriding

st clair

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Posted: 01/16/22 09:52am Link  |  Quote  |  Print  |  Notify Moderator

If they are Firestone then do not run below 5psi ever. When the truck suspension tops out it will pull a vacuum on the bags and could damage them or rip them. You need enough air in them to prevent this vacuum. It will be the same with any brand.

Guys that say bag can only stiffen the ride are dead wrong. There is much more to suspension dynamics than just a knee-jerk reaction can offer.

Your truck springs will have a neutral point, the point which the springs are neither supporting weight nor pulling in the opposite direction. This would be where the leaf springs are curved to the same shape as if they were off the truck and sitting on the ground. I do not include coil springs here as they are not necessarily attached such that they can pull.

I only have data for two-wheeled vehicles from here, but on those you can soften the suspension with a strong spring that has an opposing spring pulling/pushing the opposite direction. This set-up tends to overcome the friction in the suspension linkage that would otherwise cause you to lose some of the small bump compliance.
ON a truck there is probably a small window where you can lift the truck just past the neutral spring height where the air bag is lifting the truck and the leaf spring is trying to pull the truck back down. Opposing spring forces. Go too far and you will just get a harsher ride.

Both trucks I put bags on would ride much smoother with some air in the bags. 10-15psi on mine.

On your 1999 you will for sure have spring sag from age, so using the bag to correct the sag will both improve your ride height and maybe even handling when unloaded.

I do not make any scientific claims on truck suspension but am only comparing two-wheeled set-ups to the truck and also my personal experience that supports the fact that my trucks were smoother with air in the bags.

JimK-NY

NY

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Posted: 01/16/22 11:41am Link  |  Quote  |  Print  |  Notify Moderator

When I first bought my camper, I had the dealer finish setting up my Ram 2500. That included airbags. The ride was really bad with lots of sway. I cranked up the Rancho shocks to help. The ride became stiff and harsh and the sway was still an issue. I tinkered and found dropping from roughly 45 psi to about 15 psi helped a lot.

A year or so later one of the airbags tore. I hardly noticed the difference since I had dropped back to about 10 psi. Later I got rid of the airbags and went with Supersprings. Wow, what a difference. I was able to lower the shock settings and had a great ride with minimal sway. No more airbags for me!

On my new Ram 3500 truck I still needed a bit of help mostly to keep the headlights from pointing too high. Timbrens solved the issue. I could still aid Supersprings but I seem to be doing well without.

Grit dog

Black Diamond, WA

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Posted: 01/16/22 12:38pm Link  |  Quote  |  Print  |  Notify Moderator

RE the 5 psi thing. That is the mfgs catch all clause to keep from potentially pinching the bags under full suspension compression. IE idiot clause.
If you can fully bottom out the suspension on an empty HD truck then pinching your airbags is the least of your worries.
Vacuum pulling the bags apart is laughable.
Last truck and current truck almost 10 years combined with cheap no internet bumper bags. 0 psi empty. Hell, 0 psi even with 1000lbs ish load on the rear. Above that air pressure commensurate with the load that needs to be assisted.


2016 Ram 2500, MotorOps.ca EFIlive tuned, 5” turbo back, 6" lift on 37s
2017 Heartland Torque T29

HMS Beagle

Napa, California

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Posted: 01/16/22 02:40pm Link  |  Quote  |  Print  |  Notify Moderator

ajriding wrote:


Guys that say bag can only stiffen the ride are dead wrong. There is much more to suspension dynamics than just a knee-jerk reaction can offer.


The way they are usually installed in a pickup truck, they stiffen the ride. There is no mystery to how air suspension works, they are installed on 80% + of the over-the-road heavy trucks and well understood. Air helper springs as installed on pickups are not the same thing: they are convoluted bag instead of a rolling lobe bag, and the installed height of the bag is very low. To support a given load, the ONLY dimension that can change spring rate is installed height of the bag. At a given installed height, the spring rate will depend on the load it is supporting. In real air suspension, the installed height is typically about twice what it is on an aftermarket air helper spring. Since the travel of the convoluted bag is usually less than the truck leaf springs you more less have to inflate them to retain a ride height near the unloaded height. This will almost always increase spring rate.

Typical numbers for a pickup: rear spring rate 1000 lbs/in, doesn't change much until the overloads hit their perches. Load a 4000 lb camper and you are down 4" in the back. Typical helper air bag has 25 sq in active area each side, so to remove the 4" sag takes 80 psi. A pair of 5" high bags has a spring rate of 1000 lbs/in, added to the leaf springs (which are still there and active) gets you 2000 lbs/in total, twice the stock springs. Only if the bags were installed so that the leaf springs were inactive (very unusual!) would the spring rate be lowered.

If the air bags are used to keep the overloads from engaging it is more complicated, they may be softer than the overloads or not.

Air springs are also progressive, and short ones like those in pickups are highly progressive. The leaf spring is close to linear. So the above air bags have a spring rate of 1000 lbs/in over the first inch of compression, but 1670 lbs/in over the second inch of compression. The pressure goes from 80 psi at 5", to 96 psi at 4", to 133 psi at 3" height. This may be why they feel "bouncy" to some. The stock leaf springs would be nearly the same 1000 lbs/in over the same range, vs. 2670 lbs /in with the air bags at 80 psi nominal.


Bigfoot 10.4E, 2015 F350 6.7L DRW 2WD, Autoflex Ultra Air Ride rear suspension, Hellwig Bigwig sway bars front and rear

vern kelly

la crescenta, ca

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Posted: 01/16/22 03:33pm Link  |  Quote  |  Print  |  Notify Moderator

Balance the two airbags to give a level ride. If you have overload leaf springs, set the airbags to where the overload springs are just engaged and make sure the rear bumper is level side to side which may require different air pressure in each side. On my unit I have always had to put more in the passenger side than the driver side to level. (frig and Gen are on that side) I have Firestone ride rites.


1998 2500 Dodge V10 3.55 Quad cab. Lance 5000 camper 9'10" and tow 17.5 ft Larson Boat

Rscconrad

Illinois

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Posted: 01/17/22 08:28am Link  |  Quote  |  Print  |  Notify Moderator

For years on my 97 f350 I ran my bags at 30 pounds. Leveled me out nicely. I also have helper springs. For the heck of it I wanted to see if I could get a “softer ride. I was amazed the difference in ride around 15 psi. I was not level but not too bad and at least it pleased my wife who always complained about the rid being so jarring

zb39

slippery rock

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Posted: 01/17/22 08:29am Link  |  Quote  |  Print  |  Notify Moderator

specta wrote:

At first I thought this was going to be a political thread. [emoticon]


We need a "like" button


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bigfootford

Fair Oaks, California

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Posted: 01/17/22 11:25am Link  |  Quote  |  Print  |  Notify Moderator

F250 SWD. 4400lb camper... Air Lift bags for 20 years. Air to level 40psi. when loaded. 10 unloaded. I measured the wheel well to ground empty and that is my air up loaded level.
I also use the bags to level at a camp site. I have the onboard pump and cab control.

Jim


2000 2500 9.6 Bigfoot,94 F250, Vision 19.5, Mich 245/70XDS2's, Bilstein shocks, air bags/pump, EU2000, PD 9260,Lifeline 100ah, 200W. solar, Morningstar Sunsaver 15A/ display panel, Trimetric, Delorme/laptop, Holux gps rec,led lights, Wave-3 heat.

mellow

Salisbury, MD

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Posted: 01/17/22 02:49pm Link  |  Quote  |  Print  |  Notify Moderator

I run mine with 15psi when empty, what helped me the most was getting the rancho 9000's and setting the rear to 5 when not loaded.


2002 F-350 7.3 Lariat 4x4 DRW ZF6
2008 Lance 1191 - 220w of solar - Bring on the sun!

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