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Ask A Pro \  The weight on air bags

The weight on air bags

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teckn9ne   +1y
Ok recently i switched a friend of mines truck over from f9000's to re-7's, bag over axle setup with a triangulated four link. After the switch of course it rode a little stiffer (not a whole lot) and my question is why so? If you run a leveraged setup on an re-7 it will ride great, this is like multiplying the weight the bag sees right? So why dont i see people running say an re-6 running bag on axle? wouldnt that put more weight directly on the bag and cause it to ride a little less stiff? Also if i were to add some sort of an accumulator (like a random bag hooked up on the same airline) would it ride smoother or make the problem even worse? Theres something im missing here and i'd like to know! Thanks for the help
Bagd_Civic93   +1y
sounds like you are riding with too much pressure to have a good ride. Try letting a little air out (not enough you can't drive) and see if that works for you. My cylinders are the same way if I drop about 20psi it rides like a caddy but I i ride all up it bounces like a donk.
AVTekk   +1y
Your conception of weight is a little off man, but no worries, this is how it works... Any type of spring has a measurement of force needed to compress it, called spring rate. Airbags are no different, except for that fact that you can primarily change the spring rate with air pressure. For this discussion, the typical rule is the stiffer the spring, the more weight it can handle. This rule isnt the end-all rule because many manufacturers have dual rate steel springs with tighter windings that give a softer ride with normal driving but stiffer on large bumps to prevent bottoming out. Anyway, back on topic, since weight capacity is generally a direct result of the spring rate, we can deduce that a bag rated at a higher capacity will ride worse, at the same weight load, at the same pressure. A F9000 has a capacity of 1500lbs ea, the RE7s you swapped them with are rated at 3000lbs ea, so theyre going to ride worse unless you either add more volume (accumulators) or add more weight (a lot more weight). Why you swapped them out I dont understand because F9000s ride great and get 7.5" of lift...The design of the bags (tapered vs double convoluted) and the material theyre made from also give different rates, same thing for the shape and type of metal spring windings as well.  I mentioned volume for a second because it makes a big difference in air springs as well. You don't see any RE6s over axle because they have less volume, causing them to operate at higher pressures and a stiffer rate. They also don't get as much lift, so to get to your specified ride height, they are at a higher pressure, again riding worse. Now volume is where the tables turn a bit, because you ran go up to a RE8 and have a softer ride then a RE7 even though the RE8 is rated at a higher capacity. The reason this is true is because the RE8 has more volume and takes less pressure to reach the same ride height.Now when you put bags into a leverage setup, youre basically showing the bag more load then whats actually there, so its operating as if there is more weight on it. Since the bag is now seeing more load, its capacity is also greatly reduced by the same amount of leverage placed on it. So if the bag is directly in the middle of the bar, its on a 2:1 ratio, and its capacity is cut if half. This is an important factor is designing a suspension because if you put too small of a bag in a lever situation on too large of a truck, they will fail.
teckn9ne   +1y
Edited: 12/15/2009 8:36:24 PM by teckn9ne

So then an f9000 has more volume than an re-6? and i dont know the weight capacity of an re-6 off hand and slams site is down, appreciate the help so far!
BioMax   +1y


In many cases it would be advantageous to have a negative spring to help with ride quality, but that would take pages to try and explain why and how to properly set up. The sleeve style bags don't ride all that well without a load on them and minitrucks don't really have the weight needed to make them work properly without the negative sping I mentioned above. So your phenomenon of the convoluted bag not riding much worse than the sleeve bag doesn't surprise me.  As Dave explained, different bags have different sping rates depending on the material thickness, volume and design. So choosing the right bag can be much more complicated than you would initially think. I don't really know where to start to make any sense out of this though.
AVTekk   +1y
---------------------------------------------Originally posted by teckn9neEdited: 12/15/2009 8:36:24 PM by teckn9neSo then an f9000 has more volume than an re-6? and i dont know the weight capacity of an re-6 off hand and slams site is down, appreciate the help so far!--------------------------------------------- Theres a possibility that the F9000 has more volume, but thats not the reason it typically rides better. Its all due to the design and material in that particular bag. An RE-6 is rated around 2500lbs I believe.
Spin_155   +1y

Good answers.
teckn9ne   +1y

Yep, thanks for the time guys, it was helpful
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