Air bags on Utes , don't do it !

[Animall]

Hi guys just a heads up to all with air bags on their Utes , I work in a smash repair shop in cairns and the number of Utes we have come in with broken back is not good , air bags and overloading is a bad thing and some insurance companies are starting to refuse claims if air bags are fitted , your better off with proper uprated leaf springs as they spread the load better and don't push up against the chassis , better still is to have the chassis strengthened and blue plated as well if you regularly carry full loads and tow a heavy trailer or van , can't think of anything worse than being half way up the OTT and bang goes your chassis just because it cheaper to fit air bags , thanks for looking

[tk421]

The issue is more about overloading than the Airbags. Airbags don't magically give you a GVM upgrade. They're load levelling devices.  Yet people whack them in and assume they can add more weight. Then they start towing bloody heavy trailers too.

http://www.4x4australia.com.au/drive/1504/bent-utes/

"For another expert opinion on airbag suspension, we spoke to Beau Smith, the sales manager of Polyair Springs; arguably the oldest and biggest airbag suspension supplier in Australia. He, like me, knows of an awful lot of vehicles without airbags that have cracked their chassis. “100 per cent of photos and stories I have heard regarding this issue is to do with vehicles that are carrying huge amounts of load and/or towing. Most people that have this issue are not aware of the weight they are carrying and many are over their GVM without realising it,” he said.

Importantly he added: “Airbags are in no way designed to increase the vehicles GVM, we clearly state this on our marketing hand-outs, product packaging and instructions. From an engineering stand point, the airbags create a third point of contact (usually at the bump stop strike plate which is designed to handle severe impact) to ‘assist’ in the load carrying of the vehicle,” he continued. “In cases where we know the vehicle will constantly be on its upper limit of capacity, we recommend that the leaf pack and even shock absorbers be upgraded from factory spec for a more even load share along the chassis rail.”

[Bird]

  they are always good for a laugh!

[BaseCamp]

Hey mate - with all those bent ute chassis coming in - can you give me an indication of:

#  Total number bent that your shop has repaired in say the past 12 months.
#  How many were basic single cabs with trays; vs
#  The Tub variety; (double cab; extra cab types?)
#  Were they 2x4s; or 4x4s etc?
#  What are the insurance company(s) that are knocking back these claims - that you have seen..?


I have a single cab 4x4 ute (not the tub type) - with air bags and an upgraded leaf pack; (I think a 400kg leaf pack?) ...     I always try to make sure the ute "looks level" - and that the load is distributed across the 3 points of the bags, and the leafs ....  but these attempts are are far from an exact science - (aka "guess work").....

Hi guys just a heads up to all with air bags on their Utes , I work in a smash repair shop in cairns and the number of Utes we have come in with broken back is not good , air bags and overloading is a bad thing and some insurance companies are starting to refuse claims if air bags are fitted

[callmejoe]

Its not just utes that have failed i know of a few wagons cracking due to air bag issues as well.

[Goose]

When you say you see the utes with bent/cracked chassis in smash repairs, does that mean they are repairable and get back onto the road? I thought utes with the bent chassis where written off and scrapped.

[tk421]

Its not just utes that have failed i know of a few wagons cracking due to air bag issues as well.

Airbag issues or overloading issues?  ie what's the proof that is airbag related and not just overloading beyond GVM?  Correlation does not equal Causation.
 

No, I don't work for an airbag supplier - I'm just sceptical that its airbags causing this rather than peeps overloading their rigs. Some of whom also happen to have airbags.

[Spada]

My neighbour got home from a Simpson trip on Saturday, and his BT50 is now a write off with a bent chassis.

He doesn't have airbags, but he was loaded and hit a concealed washout at speed.

Airbags or not, it all depends on the load, and the circumstances...............

It's a bit like saying we should not fit bullbars, because we will bend the front chassis if we hit a cow.....................bulbar or not, ya cars F%&#@D because of what you did, not because of your accessories ?

[jetcrew]

If we try and keep this thread informative this will be good ...

So for the engineers out there the question I have always wanted answered is this

A leaf spring has shackles on one end and when force IE load is applied in a downward fashion the spring flattens out and absorbs some of this load through its dynamic nature ..RIGHT

No genius statement there I know  so when force is applied from underneath IE rough roads etc the spring also flattens out absorbing the load ...so it manages the upward forces and the rebound of the down ward forces

If I were to place  a massive block of wood between the centre of the dynamic and flexible spring in its centre and a solid non moveable part ..like the chassis rail  HOW DOES THE SPRING NOW WORK AS DESIGNED ?

this is not me saying this a fact or anything I just really want to know the answer as i simply cant work it out. By virtue of the position of the airbag and its design it will limit or totally stop the leaf spring from working as intended would it not ?.

I know with coils it simply slows down the rate of compression when a air bag is fitted inside the coil spring, to me this makes sense as it does not change the force direction in terms of where its placed. If i put an air bag horizontally between the rings of my coil spring i reckon i would have some major issues.

I think  personally its the design of the air bag used on leaf trucks and the way they are fundamentally opposing the way the leaf would want to work ..up and back etc  a long air bag that somehow was placed between the leaf spring and the chassis and allowed the spring to flex but slowed its rate would be better in my mind as it would compliment the leaf spring instead of working against it.

Just trying to think out loud and see what those more qualified think.

Jet
 

[callmejoe]

Airbag issues or overloading issues?  ie what's the proof that is airbag related and not just overloading beyond GVM?  Correlation does not equal Causation.
 

No, I don't work for an airbag supplier - I'm just sceptical that its airbags causing this rather than peeps overloading their rigs. Some of whom also happen to have airbags.

Hey you could be right. But same brand same engine roughly  similar  years. All 3 had airbags. Now the brand some people will say no way best 4wd etc etc. Could be right. Just strange how the 3 that i know of had airbags.

i have also got airbags, and yes i know they are to only  "help" your load NOT carry.

[Animall]

Answers to a couple of questions . Yes obviously the air bags alone are not causing chassis damage but when fitted people seem to think they can carry twice as much weight , in the last 12 month we have had about 14 Utes with damaged chassis all where fitted with airbags and all where double or extra cab . No single cabs proably because you can put more of your load in front of chassis rather than on it or behind it . All but one have been repaired ( not all buy insurance ) but once repaired they are weaker than before unless you plate the sides of the chassis which then requires a blue plate and engineering checks .but then some insurance companies will not insure because it's modified and if involved  in a accedent from the rear will not crumple as designed to and could cause more damage or injury to the ocupunts of the vehicle that hits the rear .  As for which insurance companies are not paying out I will have to find out as work on the floor not in office .

[BaseCamp]

thanks for those answers - really appreciated ...

14 in the last year from one shop is pretty bad...

As total guess work - say there is 500 panel shops in Aust and 2% are having this sort of carnage -

that makes for a minimum of 140 F-ed utes.... per year...    ??   

(Another reason to "purchase new" - if doable?)....

[Pog]

If we try and keep this thread informative this will be good ...

Hahahahahahaha.... Your always good far a laugh Jet.

Talking about bent dual cabs and airbags is always going to bring out the stories of someone's friends, uncles, mother in laws bent ute...

[Bird]

(Another reason to "purchase new" - if doable?)....

newer more modern utes would be weaker than old over engineered ones...

[Spada]

Hahahahahahaha.... Your always good far a laugh Jet.

Talking about bent dual cabs and airbags is always going to bring out the stories of someone's friends, uncles, mother in laws bent ute...

I've just spent the last few hours helping my neighbour strip his accessories off his "about to be written off" bent BT50 that does not have airbags

CAVAET- I do not possess technical knowledge on the subject, but as this is a discussion forum, here is my opinion 

I think the advantage that airbags offer, and their true design purpose, is they give you flexibility in your rear spring settings. Generally you would replace your leaf spring pack with one that is rated to the load you intend carrying most of the time. That's fine if you carry a constant load all of the time. but if you use your car as a daily runabout, and load it up for the odd trip away, you are stuck with a leaf pack that is either too harsh when empty, or too soft when loaded. Both of those scenarios are less than ideal for handling.

This is where I think air bags offer the versatility of being able to have a spring that is suited to your vehicles normal use, but gives you the ability to add a bit of air to supplement / assist the springs when carrying more load. And I'd like to stress "supplement / assist", they do not magically increase your GVM.

I agree that on a leaf sprung vehicle, where they are fitted seems to be in contrast with how the spring is mounted, but I do not have the knowledge or expertise needed to fully understand the load forces.

My assumption would be that people that are bending utes are suffering from a combination of problems like vehicle overload, airbags pumped too hard, and external factors applying additional or extreme forces to the rear suspension (cresting sand dunes at speed, severe corrugations, or sharp dips at speed).

All the examples that I've seen appear on the interweb seem to have come from areas where these types of conditions are prevalent IE;- Birdsville (utes broken on the Simpson sand dunes}, Cairns / Weipa (utes broken on the Capes corrugations}, and around areas like Frazer (utes broken after hitting washouts). These are all areas where people would generally have a loaded up duel cab towing their camper / van?

I had airbags in my duel cab Navara for about 5 years with no problems encountered after numerous trips (although I was mindful of the perceived issue and careful about how I loaded), and I have airbags in my current Cruiser wagon. In both instances they have improved the handling of the vehicle whilst towing.

I'll refer back to my "bullbar" comment in my previous post, and qualify that comment. Airbags are like any accessory that we fit to our vehicle. They have design limits and guidelines for proper use. If we use them in ways that are beyond they're design parameters, or expose them to extreme forces, then I'd expect something will break.

_{Donning flame suit and ducking for cover now....................}

[Bird]

I've just spent the last few hours helping my neighbour strip his accessories off his "about to be written off" bent BT50 that does not have airbags

[Spada]

Maybe tomorrow when we finish the job. Didn't want to offend him by taking pictures today, he seemed dejected enough 

The rear of the chassis has deflected down by about 20mm. Passenger side has bent just in-front of where the bump stop has hit the chassis rail, and the driver side is bent just behind where the bump stop has hit the chassis. The ute has aftermarket suspension with 350kg constant load springs. It's used as a work ute and is always loaded, but I suspect it was maxed (plus a bit more) for this trip, and was towing a camper.

[Bird]

Maybe tomorrow when we finish the job. Didn't want to offend him by taking pictures today, he seemed dejected enough 

that's fair enough too.... so whats he replacing it with?

[jw2170]

I also read a couple of articles recently in CT an 4WD magazines.

Reminds me of that ad for Ford Ranger, "can carry 1 tonne more than........"   

Overloading when of the bitumen seems to be the problem, I believe........

[prodigyrf]

"A leaf spring has shackles on one end and when force IE load is applied in a downward fashion the spring flattens out and absorbs some of this load through its dynamic nature ..RIGHT"
Well here's what's happening-
https://www.youtube.com/watch?v=1uRMiF2YRv0

" so when force is applied from underneath IE rough roads etc the spring also flattens out absorbing the load ...so it manages the upward forces and the rebound of the down ward forces"

Well actually the leaf springs resist the upward force progressively (softly at first and then progressively harder as more leaves come together and act as one) and they'll act equally with upward force on the 4 chassis points except for minor vector force loss acting backwards along the chassis due to the rear shackle movement (ie the leaf springs are elongating toward the rear). As for the rebound (or sudden wheel drop into a pothole) that's the job of the shock absorbers and rebound damping preventing the loaded springs expanding downwards quickly so the shockers are already acting up and down on the chassis rails in the middle of the leaf springs anyway. Ipso facto there are 3 load points on a chassis rail to be engineered for and an air bag addon would be adding to a load point with the shock.

"If I were to place  a massive block of wood between the centre of the dynamic and flexible spring in its centre and a solid non moveable part ..like the chassis rail  HOW DOES THE SPRING NOW WORK AS DESIGNED ?"

Answer is it wouldn't but would simply become a solid 3 point load on each chassis rail - ie at each ends of the spring and the now solid effective shocker and the rear shackle cannot move back and forth any longer so it's another fixed point for load.

"By virtue of the position of the airbag and its design it will limit or totally stop the leaf spring from working as intended would it not ?."

No it wouldn't act like the solid block of wood because it can work up and down just like the shocker and just like the end rubber mounted shocker it has some flexibility to move fore and aft with the elongating spring and allow its normal operation, albeit adding somewhat to the resistance of all the undercarriage being rammed up into the chassis. It's there that that the air bag would place some extra load on the midpoint of the chassis like the shock does and where you need to be careful with overloading (the same consideration would apply with pump up shocks here)

"I know with coils it simply slows down the rate of compression when a air bag is fitted inside the coil spring, to me this makes sense as it does not change the force direction in terms of where its placed. If i put an air bag horizontally between the rings of my coil spring i reckon i would have some major issues."

Well actually the air bag on a coil spring is largely acting in between the coils (squeezing out in between them) as an aid to resisting compression so again the overloading precaution applies and spada is correct with his analysis that it's nigh impossible to set sprung suspensions up for unloaded comfort and yet handle maxm loads to boot. Air  bags can assist but judiciously and you need to be aware of the tradeoff imposed over really rough stuff  ie slow down to reduce really heavy impact forces via the air bag but that also applies to the whole suspension in general. Basically you could overload the rig to a very large degree on the tar but it's the shock loads on the rough stuff that will find it all out.

[prodigyrf]

Speaking of suspension vector forces acting on the vehicle chassis with its load and passengers here's how rear motorcycle suspension (scroll down) has developed so that upward forces are split to produce some forward force that acts to thrust the bike forward rather than directly upwards like the old twin shock design-
http://www.carbibles.com/suspension_bible_bikes.html
Yes leaf springs produce a very small rearward vector force but motorcycle suspension kills that for forward thrust vectoring of the upward force although with much lighter resistive/inertia mass than a car it certainly needs to. 

[Spada]

that's fair enough too.... so whats he replacing it with?

New for old insurance coverage, so the replacement will be the same.

[MDS69]

I believe there is a vehicle manufacturer that derates their vehicles towing capacity off road.
Along the lines of what jw2170 said above it is the weights when off the black top,  even if within the GVM, making the suspension work harder and creating more stress on the vehicle.

Remember when Mercedes took those G wagons in the outback for testing and they had to keep flying in shocks because they kept failing. Precision German engineering.

[tk421]

I believe there is a vehicle manufacturer that derates their vehicles towing capacity off road.
Along the lines of what jw2170 said above it is the weights when off the black top,  even if within the GVM, making the suspension work harder and creating more stress on the vehicle.

Remember when Mercedes took those G wagons in the outback for testing and they had to keep flying in shocks because they kept failing. Precision German engineering.

 Land Rover changes their maximum tow weights from 3500kg to just 1000kg when off-road.

[prodigyrf]

Yes that's the temptation with air bag assist for initial load levelling is to believe the rig can take more load when the complete opposite is true with rough stuff shock loading. Now I recall with an early Dove and an 81' Corona wagon I added a pair of pump up shocks to do the job my coil air bags do on the Suzy nowadays. When the BIL (new pommy immigrant) was going on a first bush trip from Adelaide up to Darwin with a workmate in his small Daihatsu 4WD at the time he did likewise after seeing mine. Trouble was he was pumping them up to max to cover some mild overloading and had to limp into Alice because he'd knocked the rubber eye bushes out completely on the air shocks (nolathane bush fans take note here of another possible tradeoff)

On the flip side of the coin my old man was in charge of the survey section for the Gove mine/refinery complex back in the late 60s early 70s and they had the first small 4 cyl Hilux utes for the survey crews (bigger ones were Lite Stouts and Chrysler VJ Valiants) Trouble with the Hiluxes was they were oversprung at the rear and with only light survey gear on corrugated dirt roads were skating all over the road and downright dangerous with a couple of nasty prangs. He wanted the site workshops to take some leaves out of the springs but too busy/too hard was the reply(well you would be with Alusuisse mining engineers used to autos that drove the manual Valiants around in second gear everywhere) but one thing the construction site had was plenty of spare concrete. Some quick vol/density calcs and the right height board across the tray in front of the wheel arches and fill the front third up with conc and float her off and bobsyeruncle handling the dirt roads after that