Air bags instead of coilovers on a linked rear???

Timberwlf

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does anyone have any ideas or seen this done before??how well does it work?? I saw this on the classifieds HERE and was thinking that might be a interesting idea for my truck. any thoughts and info would be great..

later
Brandon
 

Mike_HKmtrsprts

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too funny thats my friend James old truck I havent seen that on a prerunner berfore but Camburg has air bags on their sand rail and I was told that when an air bag is compress it unloads really fast and violent causeing rebound on the shocks hard to dial....Mike
 

ACID_RAIN28

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In order to make an air ''SPRING" system work you have to understand how they work. A famaliy friend of ours has an air spring company, and on his 1980 chevy he put airsprings on the front and fourlinked the rear on airsprings, truck worked as his prerunner and daily driver for 17 years on the same springs. I bought the same springs and put them on my truck. Yes airsprings have a exponital growth rate on the spring rate, but there is a solution. Basically you are trying to stretch the rubber and at pressure you can never fully compress an airspring. What needs to be done is to set up the spring similar to a shock and resevor setting. In the top of the spring you machine and tap it to fit a -20 or larger air line to an aux air tank atleast twice the volume of the spring. So in turn it will ride softer and you can compress the spring 100% allowing you to set up a system, where the shock will do most of the work. This setup has been tested and proven, and is currently being installed in the rear of my 77 chevy.

I can hook you up with the engineering data on the springs.
Just for note, most springs have an angular capacity of 30deg at optimal psi. So a radical suspension might not always be practical.
Dave
 

ACID_RAIN28

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One more thing, the idea or the fourlink air spring rear end has been toyed with and attemped by a couple of locals, but unless done right it will not work properly. The one for sale is not one of the right ways. the other truck is in the ball park for the spring but out in the parking lot for the shock setup. I have seen that truck, he has two small springs for the bumpstops, they will burst on a hard impact.
 

Dave_G

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That's the old Enduro stadium car except John Swift was the only one who ever drove it with air bags.

Dave
 

PATCO

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Brandon, I had bags on my linked fullsize chevy. It worked well for what it was: 3400lb firestone airsprings at 2.5 to 1, Dual rancho 5000's at 2 to 1 ( rancho's?). It cycled 21", but was limited to about 17". When I built it I guessed which bags to run and was wrong. They didnt have enough rate. The truck worked incredible in small whoops, but could not take a big hit or G-out. It rode like a caddy on the street (just ask Bryce). I think airsprings can work well on a prerunner if time is spent setting them up correctly. A bypass shock might work well to control the high increase in rate. I think an accumulator tank like acidrain is talking about is the way to go. Maybe even being able to adjust the volume of the tank. I am planning on building another air setup. This time with a lot more r&d on the airsprings. I think
Greg has some bags he wants to sell. Good luck.

PATCO
 

PATCO

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Anyone know how to convert coil spring rates (lbs/inch) to airspring rates? Any engineering students want to work it out? Thanks in advance.

PATCO
 

BradM

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Air springs do not produce a linear spring rate. You would have to consider the rate at which the air bag expands with increased pressure and the volumetric change due to the change in stroke to come up with an effective spring rate. Coil springs are considered to be linear over nearly all of the available stroke.
 

kjmiller1

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I don't know anything about airbags, but have taken all the physics for engineers. It seems to me that the expansion of the bag would be somewhat linear. What makes the spring is the rubber expanding, so you have to take into account the density and elasticity of the material used to get the Elastic modulus (I think it would be bulk modulus since its volume) which would be volume stess/volume strain which is linear.
pressure = force/area
change in pressure = change of force/area
change in pressure leads to change in volume
volume strain=change in volume/initial volume
volume stress=Force normal to area A
Bulk Modulus = volume stress/volume strain
force I think is the balance between atmospheric pressure and pressure inside
area is just a little tidbit of the bag, so you would have a complicated integration equation
But all of this only has to be taken into account when designing the bag, and even then trial and error may be just as good. So my point is it is too dificult to take exact measurements off the bag to figure out the spring rate, because you'll probably screw up and be farther off then just compressing it to find the constant which is N/m^2 or lbs/ft^2, because I think it exists. Please tell me if I am way off the mark or not.
 

kjmiller1

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oh yeah, I guess the ft^2 doesn't like to be linear, my bad
 

drtdevil93

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i know nothing about airbags, but Deaver is a triangle group distributor. i can second that triangles stuff is the best there is.

erik
 

dadomin8r

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Patco: i think what you are looking to do is get the spring rate (bags) at ride height where you want it (meaning equivalent to coil rate) so you can locate the bags. This can be found on the spec sheet, I'm sure, which should give you distance from top to bottom of the bag and bag pressure. From there you will have to compensate the increased rate with your shocks. The non linear rate may be a cool way to go, but for desert, I would think that it would be pretty unreliable. Those bags heat up pretty easily, and 4-8 straight hours of dez pounding may prove to be too much for any set of bags. If nothing else, the increased heat will decrease the spring rate on the bags and may need to be taken into consideration.
 
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