Air bags on Utes , don't do it !

[Metters]

Any help comments or criticism?

These two articles are always worth a read if you just getting into caravans

http://caravanandmotorhomebooks.com/caravan-dynamics/

http://caravanbuyersguide.com.au/tow-vehicle-caravan-weight/

Another thing to keep in mine when you start changing suspension designs is car manufacturers have set their cars up to understeer since the 1950s because the average driver can not handle oversteer.  They do it placing more weight on the outside front wheel than the outside rear wheel in corners so the front tends to roll out a little wider. You redesign the springs and sway bars to transfer more weight onto the outside rear wheel in corners if you want the rear end of the car to drift out first which is oversteer.

If you stiffen the rear suspension without doing exactly the same to the front, you can easily upset the manufacturer’s front and rear weight transfer ratio and make the car prone to going into sudden oversteer. 

There is nothing unusual or mysterious about this, it has been part of the basics principles of setting up suspensions for as long as anyone can remember.

Make sure whoever alters your car’s suspension understands what they are doing and is not concentrating solely on getting the car to sit level and ride smoothly.

[Garfish]

I'm trying to find photos of my inlaws defender dual cab which bent the chassis (hit a washout) no airbags and insurance said no thanks better luck next time.


Understandable though, he had a custom made enclosed tub on the back, with too much weight at the back on a long overhang including hanging two spares off it which is why both insurance and warranty wouldn't come to the party

Since been repaired and tub shortened. 

[Rumpig]

The overhang shown on those pics posted earlier are rediculous. I'm currently getting a canopy made for my dual cab Cruiser, I shortened it's length by 100mm over a standard tray, and have mounted the spare inside the canopy on the front wall to keep weight forward as much as possible. It amazes me people don't realise how bad their set ups are, they think they can put something more suited to a single cab onto a dual cab and then not have issues. I sort of regret not shortening my canopy by another 50mm just incase, especially seeing my camper has such a heavy tow ball weight.

[Darcy7]

I'm trying to find photos of my inlaws defender dual cab which bent the chassis (hit a washout) no airbags and insurance said no thanks better luck next time.


Understandable though, he had a custom made enclosed tub on the back, with too much weight at the back on a long overhang including hanging two spares off it.

Since been repaired and tub shortened.

I'd like to see that.  If there was a chassis that I would expect could stand up to some extra abuse, it would be a Defender.  Not that they are immune to the laws of physics....!

[alnjan]

I can say with any certainty to verify the claim but after talking to a mate that had this happen to his Triton, a big part of the problem he was told comes from the alleged safety features to meet the 5 Star ANCAP rating and to achieve the required crumple effect in the rear of the utes, the target area of the bending chassis is part of the design to achieve the required crumple zone. 

So it sounds like a lot of different factors may be at play causing these problems.  People have been loading up their utes or dual cabs for as long as they have had them and worked them just as hard as they are now without the high numbers of bent chassis, so it has to be something more recent causing them to bend.  The crumple zone may be the weakening factor causing the chassis to bend. 

Just my thoughts, don't what others with more engineering knowledge think of it.

[briann532]

These two articles are always worth a read if you just getting into caravans

http://caravanandmotorhomebooks.com/caravan-dynamics/

http://caravanbuyersguide.com.au/tow-vehicle-caravan-weight/

Another thing to keep in mine when you start changing suspension designs is car manufacturers have set their cars up to understeer since the 1950s because the average driver can not handle oversteer.  They do it placing more weight on the outside front wheel than the outside rear wheel in corners so the front tends to roll out a little wider. You redesign the springs and sway bars to transfer more weight onto the outside rear wheel in corners if you want the rear end of the car to drift out first which is oversteer.

If you stiffen the rear suspension without doing exactly the same to the front, you can easily upset the manufacturer’s front and rear weight transfer ratio and make the car prone to going into sudden oversteer. 

There is nothing unusual or mysterious about this, it has been part of the basics principles of setting up suspensions for as long as anyone can remember.

Make sure whoever alters your car’s suspension understands what they are doing and is not concentrating solely on getting the car to sit level and ride smoothly.

Good points and good reads.

The people I'm getting to do it specialise in prado upgrades for Kedron.
I am also assured that the prado can handle it no trouble at all.
I am relying on others points of view to learn a bit, so this answer is exactly the type of thing I needed.
Many thanks
Brian

[Spada]

Good points and good reads.

The people I'm getting to do it specialise in prado upgrades for Kedron.
I am also assured that the prado can handle it no trouble at all.
I am relying on others points of view to learn a bit, so this answer is exactly the type of thing I needed.
Many thanks
Brian

Prado's have a coil rear suspension, so I'm guessing the bags will be fitted up the guts of the existing coil springs. That means your suspension dynamics wont really change.

The topic of this thread centres around fitting airbags to a leaf sprung rear ends in utes.

You should be fine. 

[tk421]

Prado's have a coil rear suspension, so I'm guessing the bags will be fitted up the guts of the existing coil springs. That means your suspension dynamics wont really change.

The topic of this thread centres around fitting airbags to a leaf sprung rear ends in utes.

You should be fine. 

Yup. Bags inside the rear coils on a Prado. Bump stop has to be shaved to accomodate.

[Metters]

Just my thoughts, don't what others with more engineering knowledge think of it.

It is a good thought Al but the car would still be able to do whatever the manufacturer claims.

This DVD https://www.youtube.com/watch?v=jH1Vke2Z6VY makes the problem a lot easier to understand.  The truck has its lifting cable running from the top of the jib down on an angle to the bogged car.  It simply levered the rear end down and the front went up.  The chassis was not designed to withstand forces like that.  Had the cable gone from a tow bar back to the car, there would be no leverage being applied to the chassis and this would not have happened.

A snatch strap is another good example.  They can induce staggering forces into the chassis but it does not bend.

It makes no difference whether you pull the rear end of the chassis down slowly or flex it repeatedly a short distance up and down with a lot of heavy material pressing down on the end of it, the result will still be the same

[Swogjb]

The overhang shown on those pics posted earlier are rediculous. I'm currently getting a canopy made for my dual cab Cruiser, I shortened it's length by 100mm over a standard tray, and have mounted the spare inside the canopy on the front wall to keep weight forward as much as possible. It amazes me people don't realise how bad their set ups are, they think they can put something more suited to a single cab onto a dual cab and then not have issues. I sort of regret not shortening my canopy by another 50mm just incase, especially seeing my camper has such a heavy tow ball weight.

What length tray did you go for?

I was talking to a bloke the other day who had fitted a 7' tray to his dual cab cruiser.
If that doesn't brake the cruisers back I'll eat my hat!

[Rumpig]

What length tray did you go for?

I was talking to a bloke the other day who had fitted a 7' tray to his dual cab cruiser.
If that doesn't brake the cruisers back I'll eat my hat!

wow that is asking for trouble, that's about 2100mm isn't it?...no tray as such on mine, I ordered vehicle without one. The body will be 1700mm long on mine, with as much weight as possible kept to the front of the canopy due to how far forward the rear wheels are on the tray area.

[jetcrew]

awesome info and opinions /suggestions from both experts and lay people like myself , A really good thread  ..so many of these go way off the rails and I have learnt a lot from it already and still enjoying the read  to everyone who has contributed.

Jet

[Swogjb]

wow that is asking for trouble, that's about 2100mm isn't it?...no tray as such on mine, I ordered vehicle without one. The body will be 1700mm long on mine, with as much weight as possible kept to the front of the canopy due to how far forward the rear wheels are on the tray area.

Yeah 2100mm..
Bloody ridiculous, and then to make matters worse he had a super long tow ball tongue so that tow ball wasn't so far back under the tray.

I had a custom built alloy tray made at 1700mm. Plus it sits up a lot closer to the cab than most trays.

IMO the standard Toyota trays at 1800mm are just to long.

[alnjan]

It is a good thought Al but the car would still be able to do whatever the manufacturer claims.

Interesting word that one, Would, up there with Should.   

The example in the youtube clip was doomed to fail and have seen similar vids.

Personally I think there is more than one factor at play causing the bent chassis phenomenon and until it is seriously looked at with all factors taken into account it will continue to happen at the alarm and distressing rate. 

I do believe the loads and load placement do have a very large bearing on the problem.  As in the example you gave above with the brick, most utes/dual cabs can carry a 500kg load with no damage, but is that a static 500kg or a dynamic 500kg load.  You don't hear of too many bent chassis on a dual lane highway compared to some of the more less maintained roads.

[Metters]

but is that a static 500kg or a dynamic 500kg load. 

They will all support a lot more than 500kgs while sitting still.  It is the dynamics that cause all the problems.

The manufacturers are not going to do anything about it.  They decide what price range and segment of the market they want the car to compete in.  They design it, build it, test the prototypes to destruction then put it onto the market.  If someone takes it outside its design limits and breaks it, it is not their problem. 

It is no different to fitting a turbo to a non turbo engine then breaking the pistons.  It is not the car manufacturer's fault, they design their turbo engines from the ground up to run with one.  They don't simply bolt one to their non turbo designs.

  You don't hear of too many bent chassis on a dual lane highway compared to some of the more less maintained roads.

You are right and that is why the manufacturers will tell you to reduce weight on off road conditions.  All of this nonsense about GVM upgrades and heavier suspensions is just asking for trouble.

The advertised maximum towing and carrying capacities are for the highways only and I don't mean the Gunbarrel type.

Every manufacturer is capable of building a car that will never break.  The only problem is few people would be able to afford to buy it.

[Metters]

They will all support a lot more than 500kgs while sitting still.  It is the dynamics that cause all the problems.

The manufacturers are not going to do anything about it.  They decide what price range and segment of the market they want the car to compete in.  They design it, build it, test the prototypes to destruction then put it onto the market.  If someone takes it outside its design limits and breaks it, it is not their problem. 

It is no different to fitting a turbo to a non turbo engine then breaking the pistons.  It is not the car manufacturer's fault, they design their turbo engines from the ground up to run with one.  They don't simply bolt one to their non turbo designs.



You are right and that is why the manufacturers will tell you to reduce weight on off road conditions.  All of this nonsense about GVM upgrades and heavier suspensions is just asking for trouble.

The advertised maximum towing and carrying capacities are for the highways only and I don't mean the Gunbarrel type.

Every manufacturer is capable of building a car that will never break.  The only problem is few people would be able to afford to buy it.

[alnjan]

Yep gotta agree with you on that.  Just seems people just have to take everything and not the minimum when they go tripping around these days

[oldmate]

awesome info and opinions /suggestions from both experts and lay people like myself , A really good thread  ..so many of these go way off the rails and I have learnt a lot from it already and still enjoying the read  to everyone who has contributed.

Jet

X2

[grafy82]

Just thinking out loud, could we assume that we won't see this sort of damage under similar loads and road conditions with the new Navara seeing as though it has rear coil springs?

[Metters]

Yep gotta agree with you on that.  Just seems people just have to take everything and not the minimum when they go tripping around these days

There is nothing wrong with taking everything you need.  The trick is to choose a car that will carry the lot without modifications and still have plenty left in reserve when you take it into the rough stuff. 

This discussion brings back memories of the 1953, '54 and '55 Redex trials.  Have a look at the damage suffered by many cars on this results sheet. http://www.uniquecarsandparts.com.au/redex_1955.htm      Click on the BACK or NEXT arrows on the bottom of the page for more information if you are not familiar with these trials.

Local people were driving the same cars on the same roads or tracks without having all of these problems.  The difference here was not excessive weight but excessive speed.

With modern 4wds the problem is maximum weight combined with incorrect weight distribution with maybe a just a touch of too much speed in some cases

[Bird]

There is nothing wrong with taking everything you need.

agree... its the ones that take everything they need and twice as much Shit as they don't need...

[Metters]

Just thinking out loud, could we assume that we won't see this sort of damage under similar loads and road conditions with the new Navara seeing as though it has rear coil springs?

They won't make any difference.  The problem is what is on the end of the chassis back past the axle.  When the chassis falls and is eventually brought to a stop by the springs, bump rubbers or aftermarket air bags, whatever is behind the axle does not want to stop.  It thumps the end of the chassis down hard if the material on it is heavy enough.  The chassis then tries to pivot on the axle and tries to lift the other end. 

It is the same if the front of the chassis drops down.  It pivots on the axle housing and instantly tries to lift the rear end .  If the forces generated are beyond the chassis's design limits, it wll bend.   It is heavy material on the end of a lever that is causing all the problems.  The lever is the distance from the axle back to the material.

Springs can't stop that.  Moving the axle back to the far end of the chassis would because there would be nothing extending out the back unsupported.  That is probably not all that practical though.

You could try a simple little test of this with an egg carton.  Place two eggs in it at one end only.  Hold the end of the carton with the eggs in it against your body in a horizontal position with your thumbs on top and a couple of fingers on each hand under each side of it.  Rock your fingers slightly so the other end of the carton moves up and down.  Note how it feels than turn the carton around and do the same again. 

You will notice a considerable difference when the eggs are further away from your hands.   The heavy end of the carton does not want to stop when it is going down and it is harder to lift it up quickly.  That is what is happening to the end of your chassis.  It has been designed to resist a certain amount but it will bend if it is excessive.

I think a lot of aftermarket suspension advertising has lead many owners to believe they can put anything on the back of their car and the suspension will fix it.  It will lift the car and maybe improve the ride but it can not remove the excessive weight way down the back that is flexing the chassis up and down beyond the limits that the factory engineers designed it for.

[GeoffA]

There is nothing wrong with taking everything you need.  The trick is to choose a car that will carry the lot without modifications and still have plenty left in reserve when you take it into the rough stuff....

Correct.

This is where trailers can come into play (with sensible ball weight). I shudder to see the way some load their cars.
We take everything we need, and also cater to some extent for others.
If one of our travel companions is stuck, then so are we.....

[alnjan]

It is a bit like doing the maths in this link

https://practicalmotoring.com.au/car-advice/why-a-3500kg-tow-rating-may-not-really-be-a-3500kg-tow-rating/

How many of us have actually loaded up vehicle and trailer and gone to the weighbridge to establish our

Tare (or kerb) weight – how much the vehicle weighs
 
GVM (Gross Vehicle Mass) – or the maximum the vehicle can legally weigh.
 
Payload – the difference between the GVM and tare.
 
Front and rear axle load – how much weight can be placed on either axle.
 
Braked tow rating – how heavy a trailer the vehicle can tow
 
GCM (Gross Combined Mass) –  How heavy the combination of the vehicle and trailer can be.

And throw in your ball weight to good measure.

I dare say if we did this we would probably scare ourselves.


 

[alnjan]

This one covers trailers

https://practicalmotoring.com.au/car-advice/everything-you-need-to-know-about-towing-heavy-trailers/

I guess it comes down to the magical art of where and how to pack your load