Stacked airbags

[jeromio]

I've been searching all over for this and I've come up completely empty. It seems (to me) like an obvious solution to the problem(s) of airbag suspensions: the less air pressure, the lower the ride height AND the lower the spring rate. So, super low, you're either on the bump stops (not good), or you're warbling all over with no control (also not good). And then the reverse: max ride height is also max spring rate (jacked up but way too stiff).

So, I'm wondering why you can't just stack 2 airbags, meaning individual airbags each with their own separate air inlet (one on top and one on the bottom). So with one bag completely aired out, the ride height drops, but the 2nd bag provides a relatively usable spring rate. One spring maxed out for lift would leave the 2nd to provide some compliance.

Why is this not something that you can just order off the shelf? Am I missing some important detail?

[PDW HOTRODS]

Wouldn't stronger shocks and a sway bar fix the problem? get taller air bag or position it so it is not maxed out at the highest you want the truck. Stiffer shock and sway bar should keep it from moving around too easy and feeling like riding on a marshmallow.

[SCOTI]

Originally Posted by jeromio

I've been searching all over for this and I've come up completely empty. It seems (to me) like an obvious solution to the problem(s) of airbag suspensions: the less air pressure, the lower the ride height AND the lower the spring rate. So, super low, you're either on the bump stops (not good), or you're warbling all over with no control (also not good). And then the reverse: max ride height is also max spring rate (jacked up but way too stiff).

So, I'm wondering why you can't just stack 2 airbags, meaning individual airbags each with their own separate air inlet (one on top and one on the bottom). So with one bag completely aired out, the ride height drops, but the 2nd bag provides a relatively usable spring rate. One spring maxed out for lift would leave the 2nd to provide some compliance.

Why is this not something that you can just order off the shelf? Am I missing some important detail?

They probably don't make such an animal because of lack of demand. How many people would need the set-up to creep 1" off the ground @ optimal pressure & then later that day need it @ stock right height again @ optimal pressure? It wouldn't be just the springs.... You'd also have to dial in shock travel heights. And, you can't align it for both. Which height would you be aligning it for??

Beyond that, the end-plates of the bags would have to be built so they can be stacked some how or an adapter made allowing two to mount together. Bags @ normal lowered ride height & optimal pressure are typically 5" minimum up front so x2 would be 10" of spring you'd have to figure out how to fit. Some sort of crossmember mods would be required which would possibly lead to other required mods.

They make triple bellow bags but again you'd have to build the vehicles mounting set-up to work within the range of the air spring. Then those shock & alignment concerns would need to be addressed as well.

There is a set-up that allows you to build @ a 'lowered' height & then switch to 'dummy-low' @ the touch of the finger w/the exact same ride quality. Alignment configurations can be built so the impact is minimal. The problem is the price of entry to the club as it's exclusive from the perspective of the blue collar builder.

[Ziegelsteinfaust]

On Finnegans garage a couple years back. They put hydraulic coil overs on his 67 truck.

The hydraulics controlled ride height, and the coil over portion controlled spring rate with dampening.

That's probably the closest thing to what you described.

[SCOTI]

Originally Posted by Ziegelsteinfaust

On Finnegans garage a couple years back. They put hydraulic coil overs on his 67 truck.

The hydraulics controlled ride height, and the coil over portion controlled spring rate with dampening.

That's probably the closest thing to what you described.

This is exactly what I described. Bring your big checkbook to the table though....

[Richard]

Remember seeing something a while back about a rear high lift fad with bags. Yes, you can double the lift from the bags. The ones I saw used a wishbone link to a coupler piece in-between the stacked bags. This would be needed because the setup would want to fold out in the center.

[Ziegelsteinfaust]

Originally Posted by SCOTI

This is exactly what I described. Bring your big checkbook to the table though....

Sure it is expensive, but compared to an all-in top shelf air ride kit. Not that much more.

Is it better? Depends. As anything this does is not something I am looking for.

I have had a air ride for a minute, and the way I use my vehicles. This is the optimal choice for me.

[SCOTI]

Originally Posted by Ziegelsteinfaust

Sure it is expensive, but compared to an all-in top shelf air ride kit. Not that much more.

Is it better? Depends. As anything this does is not something I am looking for.

I have had a air ride for a minute, and the way I use my vehicles. This is the optimal choice for me.

Hhmm.... I've seen that the shock set-up alone was over $4k (the 4 shock/coil-overs). Then you have to get the control management & hydraulics (unless that was included in the cost but not communicated). I've yet to see a price tag for the control side of the Hydroshox set-up.
*EDIT* The Hydroshox set-up includes the pump & management systems w/prices starting @ $5k ($4995.00).

JRI's version starts @ $6k for non-adjustable shocks.

The Accuair set-up was what I would consider top-tier & was around $2k which included management & electronics. Bags & shocks can be obtained for under $1500.

[jeromio]

The hydraulic over spring lets you adjust ride height, but not spring rate. Air springs *can* do both, but the spring rate adjustment adds height, which is not typically what you want. Yes, the shock rate will always be the same, but that is also not generally dependent on change in ride height (provided the shock has the travel on the upper and lower end of height).

There are systems that do air over spring, with the aired out spring being the "default" and you air up to go over obstacles (eg lowered car not being able to make it over speed bumps). I'm talking about something similar, but with air over air. In my imagination, this allows for much more flexibility. With 2 springs at "medium" inflation, you could be at optimal ride height. But you could swing the pressures across the 2 bags and gain or lose compliance without drastically affecting ride height. Or you could navigate a nasty dirt road without dragging your longtubes in the gravel.

True, it is more complex: twice the number of bags, valves and pressure sensors. I don't think the stacked bags would be any more prone to "folding" than a dual bellows spring. Attaching the 2 springs together is not that difficult a problem. The main problem is sourcing the correct short air bags w/ the appropriate load handing and then ensuring there's enough room in the cavity for the taller spring. Shortest springs I've found are min 3" though....

[SCOTI]

Originally Posted by jeromio

The hydraulic over spring lets you adjust ride height, but not spring rate. Air springs *can* do both, but the spring rate adjustment adds height, which is not typically what you want. Yes, the shock rate will always be the same, but that is also not generally dependent on change in ride height (provided the shock has the travel on the upper and lower end of height).

There are systems that do air over spring, with the aired out spring being the "default" and you air up to go over obstacles (eg lowered car not being able to make it over speed bumps). I'm talking about something similar, but with air over air. In my imagination, this allows for much more flexibility. With 2 springs at "medium" inflation, you could be at optimal ride height. But you could swing the pressures across the 2 bags and gain or lose compliance without drastically affecting ride height. Or you could navigate a nasty dirt road without dragging your longtubes in the gravel.

True, it is more complex: twice the number of bags, valves and pressure sensors. I don't think the stacked bags would be any more prone to "folding" than a dual bellows spring. Attaching the 2 springs together is not that difficult a problem. The main problem is sourcing the correct short air bags w/ the appropriate load handing and then ensuring there's enough room in the cavity for the taller spring. Shortest springs I've found are min 3" though....

3" minimum compressed & 5" @ recommended ride height pressures.

5" @ recommended pressure + 3" @ full compressed height = 8" of stacked height w/the 2nd bag on the bump-stop. Add in some height to get it off the bump stop & you're over 8" of height w/a larger OD cavity required than a traditional coil spring (or coil-over). Yes, one could do 4" (primary bag) & 4" (secondary) but again you're not @ the height/pressures that are likely spec'd.

Seems finding the space to fit a set-up like that up front might also be as crucial as sourcing the correct air bags. Let us know if/when you figure out a solution & get it built.

[Richard]

Would think that stacked bags would act the same as the separate coils on my coil over shocks. Each spring (or bag) sees the same amount of weight. For example my stacked 250 lb springs would compress 1" for each 250lb of weight. 1000lb weight each spring will compress 4". Total spring height for both springs will reduce by 8". This method effectively reduces spring rate by half. Have a 125lb spring rate. Changing spring rate in one spring will just raise or lower the effective spring rate (raising or lowering pressure in one bag). Some coil over shocks such as mine have stops for one spring. I can set the point my spring rate changes from 125lb to 250lb by stopping movement of one spring. You would need to stop movement of one bag at a point to increase spring rate. Bottoming out one bag would accomplish this. FWIU stacked bags would decrease spring rate not increase it.

[jeromio]

No, that is true: stacked springs will be "softer". Which does make sourcing the correct bags even more difficult, as Scoti points out.

I think what I'm probably more likely to do is bag + spring bc I'm for sure not gonna get custom bags made.

[Richard]

Should still work with standard type bags. Coils are linear and fairly predictable as they compress. Air bags increase in pressure as they compress, a progressive spring. Finding the correct separate pressures to run for a smooth transition from two bags to one will take trial and error. Using a coil in place of one spring will still make things unpredictable as the air bag compression relates to pressure.