………Like folks talk about oil, tires, waxes and whatever…..there are personal choices you feel is best and you propose that idea to others with your evidence, the rear air ride suspension has hit this personal choice plateau. Whatever the reason you hear be sure you make YOUR decision on this super important component on you coach based on real facts, design, reliability, serviceability, performance and safety and not what it sounds like others do!
The original air bag system was awarded to the lowest bidder. That’s not to say its a bad design but as in most things there were good and bad points.
When Firestone (the original system designers ) stopped production of the original air bag design guys came out of the woodwork rigging up similar single air bag systems to retrofit working similar to the original bags.
Some were big fat bags that came perilously close to hitting the wheel well and tires. The brackets were offset because of this causing all sorts of stress issues! Some have huge spacers on the sides to make up for the smaller bag length. All of those options used the same single bag hookup which carried on the basic positive aspects but also carried on the negatives of the original design.
Honestly, I’m tired of guys saying they like this Or that system based it seems on the same non technical personal preferences that other people say and have repeated. These recommendations seem to be made on personal things like what you did based on what your friends did or what seemed popular. None of the replica single air bag systems out there were designed and assembled then computer tested to assure it was safe and of superior construction and operation.
This is the wrong way to make such an important decision. I also must tell you sometimes buying something based on price is what you do. On such a technically important component, cheapest is not the best parameter to use in this decision.
Some say they all hold up the back of the coach and that would be right. The system however is not a static mounted device. Its operation is dynamic based on what the system is presented with and all of these replica systems have issues that really should not be assumed work as fine and safe as any other system.
I’m not saying this to try and sell you a quad bag rear suspension…I don’t produce or make the profit from it it but I WAS involved in the design of the system as were several other GMC enthusiasts who, tops in their technical fields, added to the design, manufacture and testing and I KNOW the system is safer, better designed and operates mechanically superior. This is not my personal feeling though I was involved in its design, I say it’s a superior product based on the design, testing and a decade of real world testing in the field on coaches.
The quad bag system is a discrete system with each wheel having its own independent moving assembly which absolutely gives a more stable ride….. especially when towing. Its designed to do that and it works…….of this there is no question.
Being independent, the wheel vibrations from many issues does not “talk” to the adjacent wheel where if bad enough an oscillating vibration sets up between 55 and 65mph. This is a completely true statement.
Original nominal air bag pressure was @110psi. The Quad bag nominal pressures hover @ 75 pounds meaning there is less coupling of vibration from the rotating assembly to the frame and body…….and you!
Also true the quad bag offers a safety issue no other bag system can say. If you loose a rear wheel for whatever reason….tire, bearing, spindle failure, wheel comes off, flat or whatever you will be on the side of the road…usually in the ants having to effect some repair to move or your coach will need to be cradled on a flat bed trailer because your coach cannot be towed on the ground or even moved! A quad bag system can have a wheel on 1 side or even both sides actually be taken off of the coach and your coach can still motivate. A huge advantage? Yes for sure. The first time you have to deal with any rear wheel issue on the road you will say Ah-Men brother to this issue.
Then when it comes to serviceability, only the quad bag system was designed to accept a standard design air bag configuration…..not some one bag that happens to fit. Firestone, Goodyear, Continential, Air Lift or indeed any center line fitting in line bolt on and connection air bag will fit. The 2 piece 54 pound each side 3/8″ zinc anodized support structure was computer tested to failure and will not fail in this application….this is also an important fact that none of the original replica bag systems offered can say.
Why is this testing important? The operation of the rear suspension is a dynamic, 3 dimensional movement design that does much more than simply hold the ass of your coach up. Turning with a tandem design suspension puts lateral pressures none of the other air bag designs address.
The 2 wheels on 1 side of your coach twist to relieve side pressures set up from the tandem relation of the wheels. A big fat bag may distort and hit the inner wheel liner or even in some cases the tire. The skinny little bags with big spacers on each side of the bag creates a side motion they were not designed for. Go make a wide sweep in a parking lot and you will see what I mean. Air bags were not designed for such lateral pressures. This is why the original single air bag differs greatly from these current air bags used in this application. That’s why the bags were loaded onto those big aluminum cones.
And the system with 2 bags on 1 side connected with a moving center plate tries to rip the pivot point apart from these lateral pressures. Today’s air bags are not designed to move in all directions on both sides.
All of these facts are not personal preference or from what the most vocal person says. These are documented facts
Another documented fact is the quad bag system will cost 2 times as much as any of the single Bag rehash systems. The quad bag system is shipped in 2 boxes weighing 54 pounds each! By the pound its a better deal but beyond that you are relying on tested and documented superior design.
It’s always folks buy more of the cheaper of 2 options…….in this case you are not getting more performance, safety and reliability and serviceability using the other systems.
Now it’s true folks defend their decisions and think everyone needs to do what they did. Sorry but I do not recommend going cheap on this system. The reason I am spewing all of this here is I feel social media is not doing a comprehensive job of exposing to those that truly want to know what rear suspension system is better. I say “better” NOT based on a personal preference based on someone’s taste or what they did. I am not meaning to rain on the price parade but all of these rear suspension systems are NOT created equal to a Quad bag systems having similar outcomes. This is a real…hard fact that the next generation of GMC owners needs to hear and understand.
This predecessor earlier design “4 bag system” was NOT computer tested and does have its own set of issues. Nominal bag pressures on that system surpass 135psi and the rated bag pressure specification of the bags used! The current “quad bag system” is not from that design and other than having 4 air bags differs greatly.
It has a stable ride but its stiffer and requires more bag pressures than the air giving a stiffer, vibrating ride. For this and other technical reasons it too have drawbacks that effect its performance.
If you are up against a rear suspension decision, don’t buy on prices, don’t buy because someone else said it’s “great”. Ask them why they got it and if the first reason is price…..don’t follow blindly. And in this case if it sounds like what everyone is doing on Facebook know that’s because those threads are louder and politically connected. This important suspension decision needs to be based on more than that because this decision is much more important than that.
If you scoff at what I say or think I’m attacking one system please do some independent investigation. Not hearsay. If you don’t like me or whatever….. …buy the system from Applied GMC , they build and sell the system…..I buy the system from them! I do not produce the system. Many serious GMC enthusiasts put their heads together and I have to again say it’s superior not because i say it but because it really is!
So sitting through this diatribe I hope I have given you a needed contrast to the social commentary that social media sometimes makes you think is the right way to go. Base this decision on facts, technology and safety. Remember “The emperor is wearing no clothes” if you know what I mean.
So I’ll stop this verbiage assault on your eyes and brain, go look at something soothing to get all of this out of you head but do not forget, do not base your rear suspension choice on popular demand. Hey, who SAID maintaining a GMC Motorhome would be cheap or easy?
Thanks for putting up with me and thanks for dropping by…………
I’ll shut up now and go back to my shop
###So in editing then rereading it twice I can see I’m endangering pissing off way more people than if I had not said all this and for that I in no way meant to attack anyone or anything. And hey, I have an original 2 bag system on my baby
so I’m not attacking….um sorry it probably came out that way but do look many of the threads about the air ride systems or some other issues for that matter……social media makes lasting impressions in short snipit stories at best not leaving air to dig deeper.
Maybe I may be attacking social media in a way in that trends flow with the wind…..
Wow, don’t know why my type just freaked……..musta pushed something………… So do what you want, stay safe and investigate. There’s more to this subject than looks.
Since I’ve written “Gone With the Wind” here, let me also say we’ll have a get together at the upcoming GMCMI convention next month where I’ll be the target for anything you would like to talk, argue, come back at or just see how many feet I CAN actually fit in my mouth! I’ve asked to schedule it to give equal rant time for the gals in the crew and not have anything else scheduled so you can come. Hey, the guys KNOW they will live forever and their beloved coach will NEVER let them down! I want you there! I asked to make the subject “So what’s next”. Should be good intermission entertainment between some of the tech stuff……. I appreciate all of you putting up with me and all the Crap I spew out sometimes. I don’t mean anything and only want to help.
My fingers are tired but I felt I had to try and redeem some of my integrity……..see ya later
