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

[Timberwlf]

does anyone have any ideas or seen this done before??how well does it work?? I saw this on the classifieds HERE (http://www.race-dezert.com/cgi-bin/ads/atl.cgi?ct=2&md=second&id=5791) and was thinking that might be a interesting idea for my truck. any thoughts and info would be great..

later
Brandon

[Mike_HKmtrsprts]

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]

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

[Salvador]

Check the attached photo, theres a few more on the 2002 Fud New years Photo section on page 2.

[ACID_RAIN28]

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.

[1992f150]

funco runs airsprings on their buggies....
http://www.funco-motorsports.com/long_travel_suspension.htm

[Dave_G]

Kind of like this air bag?.....


Dave

[Mike_Cohen]

Dave,

Us that a photo of the Enduro Fairway Stadium Truck? I can remember Ashley skying that thing at the "SKY Tower" at Glen Helen back in the day?

Mike Cohen

[Dave_G]

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

Dave

[PATCO]

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

[ACID_RAIN28]

AIR SPRING INFO (http://www.firestoneindustrial.com/firestoneindustrial.htm)

Here is a link to the Firestone website that has all the airsping info you could ever want. I would say firestones are the best despite the exploding tires.

[tedmales]

the best are triangle spring. they are what the big trucks use. firestones are all right, but triagle is better, and if your going to use a regular bag, nothing to exotic, slam specialties is the best

http://www.trianglegroup.com/

http://www.slamspecialties.com/s_compare.html

[PATCO]

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

[Kritter]

What are the units?

[BradM]

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]

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]

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

[drtdevil93]

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]

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.

[ACID_RAIN28]

GO TO THE LINK THAT i HAD A FEW POSTS BACK IT HAS ALL THE CALCULATIONS, CONVERSIONS, AIRSPRING HARMONICS, ETC!

[1992f150]

acid Im reading thru that site but the information is kind of scattered, mostly talking about their products insted of general info.
Here is a (dumb) question but what if you used an air filled shock type of spring insted of a bag? it would certainly be easier to set up....or does the shape of the rubber bag make the ride better?

Oh yea, also how does cost of a shock + airbag compare to a coilover shock + coils? Im not sure on the price of these air bags.

[ACID_RAIN28]

Fox offers a 2.0 airshock they are more efficiant than an airspring setup but I don't know that much about them.
Air springs for the front of a truck would be about $100 each and about $100-120 for the rear.
plus you don't necessarlly have to clutter the truck with tubing, you can do a good four link system and four corner airspring setup with no holes in the bed and a light hoop in the front.

I got an engineering manual from them and it gave me all the available types of airsprings as well as all the math behind any setup.

[kjmiller1]

I may have interpreted your post wrong, but are you saying that the fox air shocks can be used instead of the air bags? If so, do they work like longer air bumps and look similar to shocks? I'm trying to picture in my head how they would work and have a decent stroke length, but my brain is tired from all my homework http://www.race-dezert.com/vb3/attachments/old/images/graemlins/confused.gif

[desertracer]

On the front end of our Jimco, we have a 12'' fox coil carrier air shock. I'm not sure if this is what you are taking about here. We only run about 30-40 psi in it along with a single spring. This set-up helps to keep the car from compressing too far into the travel through the whoops and allows it to sping up quicker. Some don't like air shocks on race cars but thay obviously do work well when set-up properly.

[ACID_RAIN28]

No I was refering to the fox airshock with a smooth 2.0 body with a 1.25" shaft, they cost about 200 or so and come in a range of travel like 4 to 14"

[dadomin8r]

Marivin Shaw used to make something like that a long time ago for motorcycles. It was a nitrogen filled air spring/shock. one unit did it all. I was watching some hee-haw monster truck thing on discovery and they are using Nitrogen powered springs. They look like a shock but they are a spring only. They said that a problem they have with them is that, like stated with the air bags, they do not provide a linear rate and are hard to set-up properly.

Check out this pic of the marvin shaw:
http://www.marvinshawshocks.com/pictures/cruiser4.jpg

PS - I don't know if anyone has tried them, but it looks like Shaw makes bump stops for $319/pair:
http://www.marvinshawshocks.com/pictures/bumper.jpg
or $179 each:
http://www.marvinshawshocks.com/pictures/billetbumpstop.jpg

ANYONE TRIED THEM?

[ACID_RAIN28]

My friend ran the bumpstops on his truck, they worked fine, the problem with the marvin shocks is the rod ends are way to small, not for heavy use, this buggy company I used to work for tried to get them with bigger but they wont do it.

[ranger09]

hey what about using these?

https://www.universalairsuspension.com/images/COILOVER.gif

[14802]

Wow old thread. but they might work great on a FUNCO buggy

[151fab]

I think in the case of the king shock, your using the air-bag for load leveling and ride height adjustment. I'll probably get alot of crap for saying this but I don't see the advantage to using air when a coilover is more compact, way more tunable and predictable, and less prone to damage. But, for a dual purpose vehical those things might be the ticket. Imagine those on the back of a prerunner/parts-getter. With an onboard air compressor and those units at the rear of your truck you could air-up, toss in your bikes/quad/parts, get to the location and then air-down and boogy. I just talked myself into looking at those for the Bronco... Cool

[151fab]

The more I think about it, the more I like those things!!! Cool find Ranger09!!!

[Ramsey_ElWardani]

Why not just use a Coil Over Air Shock? Infinate spring rate and curve combinations. I love them!

[partybarge_pilot]

Why not just use a Coil Over Air Shock? Infinate spring rate and curve combinations. I love them!


Heat=spring rate change. Lots of pressure= seal stiction.....

[Ramsey_ElWardani]

Heat=spring rate change. Lots of pressure= seal stiction.....
You are right. We don't experience much heat change and they are very predictable. It has not been a problem in thousands of miles of racing. I wouldn't do it any other way after the positive experience I've had the last two years.

[Ramsey_ElWardani]

Reply to deleted post:

They are on the Kupiec Class 8. We have never had a failure or leak. I have a spreadsheet with graphs that gives me exact tuning information. At Laughlin on Saturday I averaged 44.3 Mph, which would have put us 14th in the TT's and 5th in the Class 1's; so you can see the setup works. There is some video at http://www.fw-productions.com/movies/laughlin07hi.wmv

P.s. The faster Class 12 and 1600 winners averaged only 41.9 and 41.3 respectively.

[therail]

Heat=spring rate change.

Use nitrogen.

[partybarge_pilot]

Don't get Me wrong, I like air springs. It's just given the choice I would run an airbag over an airshock. I had a Toyota with a 4 link on airbags. Worked very well for how little I knew about shock tuning at the time.

Always used Nitrogen in the bags. Rate change was as simple as putting a little antifreeze in the bags.

[therail]

Why antifreeze? Why not an oil?

[partybarge_pilot]

Any non corrosive liquid would work. Some oils may not be 100% compatible with the rubber that the bags are made from. Firestone recommends antifreeze. Plus it's easier to pour.

[Scott_F]

Anti-freeze is the way to go to modify the air spring rate. It reduces the inner volume, which makes the spring rate more progressive. Air springs are non-linear and progressive, which varies according to pressure. And for those who think a linear spring rate is the preferred setup, why is virtually every off road vehicle sporting dual rate springs? It is so they can have a crude way of achieving a progressive spring rate. And why are coilovers cantilevered or canted inwards? To provide more progression in damping and spring rates. Likewise, dirt bikes usually have a straight rate rear spring, but a linkage which provides a rising spring rate. Rising rate is king!

[ranger09]

no really what about using these?

https://www.universalairsuspension.com/images/COILOVER.gif

im thinking about it on my friends linked ranger. should i set it up as if it were a regular coil over?
thanks

[Bulldozer]

They're probably alot more complicated to setup then a regular coilover.

I don't really see the point?

[DirtyD]

This is definetely an interesting thread to me. I designed this set up for my truck some time ago and finally got it together and out to test. Although my wheel travel is way limited by the temporary shock set up i'm using for now, it works pretty good as is so far, and the "spring rate" seems to be "in the ball park". It is good to learn that I can adjust my bag spring rates with added air volume or by adding fluid to lessen air volume. I will be running 18" travel shocks when I can squeeze out the dough for them and it will cycle 30" of travel.(now i'm at 16") I'm using 8018 firestone triple bellow bags and running them to their maximum 30 degrees of angularity on the in board cross beam a arms at full droop at about a 2-1 ratio to the actual wheel travel. This design was a little more complicated than locating the bags directly on the control arms but the idea was to keep the bags up out of the rocks and to do something a little different with full function. I have never used air bags offroad before so we will have to see if it will stand the test of time and abuse, but that is what it has in store for it so we will see how it goes!

[Grunion]

here is a pic of mine
http://grunionfabrication.com/Gallery/albums/album138/cbrown005.sized.jpg

[DirtyD]

Looks good. Got any more pics?

[motochris]

This is definetely an interesting thread to me. I designed this set up for my truck some time ago and finally got it together and out to test. Although my wheel travel is way limited by the temporary shock set up i'm using for now, it works pretty good as is so far, and the "spring rate" seems to be "in the ball park". It is good to learn that I can adjust my bag spring rates with added air volume or by adding fluid to lessen air volume. I will be running 18" travel shocks when I can squeeze out the dough for them and it will cycle 30" of travel.(now i'm at 16") I'm using 8018 firestone triple bellow bags and running them to their maximum 30 degrees of angularity on the in board cross beam a arms at full droop at about a 2-1 ratio to the actual wheel travel. This design was a little more complicated than locating the bags directly on the control arms but the idea was to keep the bags up out of the rocks and to do something a little different with full function. I have never used air bags offroad before so we will have to see if it will stand the test of time and abuse, but that is what it has in store for it so we will see how it goes!

Dang.....that sure looked like alot of work. Interesting, thanks for the pics.

[partybarge_pilot]

I don't really see the point?


Change your pre-load in seconds without tools..........

[jesusgatos]

I'd use airbags on a long-travel chase truck or a prerunner that I wanted to be able to haul dirt bikes with...

[DirtyD]

Dang.....that sure looked like alot of work. Interesting, thanks for the pics.

Definetely alot of work. Hopefully they will work out reliably or else I'll just have to rip out the bags and slap some FOA coil overs on there and call it good. ;)

[Grunion]

http://grunionfabrication.com/Gallery/albums/album138/cbrown008.sized.jpg
Looks good. Got any more pics?

[DirtyD]

Nice looking set up. Looks like you've put some miles on those bags. Apparently they are working out pretty well for you. How is the rear done?

[151fab]

I've said it befor, Grunion you better not change that paint, it's perfect just as it is.