Poly air

Wayne i think he want's to use both and want's to know if that would be overkill, that is a lot of weight over the ball, is that legal for that vehicle ?

Baz,

Good point about the ball weight. The rating on a coil cab is only 200kg. On the LWB it is 350kg.

The ball weight seems high. With that amount of weight only a large/ heavy 4WD could tow it.

Wayne.

I also have Polyairs and they are a great improvement on the Explorer and if they improve the Explorer got to be good for the so called better 4x4s (though the other half hasn't tested them under load yet lol) fits a lot of gear in such a small space !!!!! all jokes aside ball weight could be a problem unless you have the LWB.

Mate, if you are concerned about the off road clearance you shouldn't be thinking about Poly air bags at all. If you are going to do long trip fully loaded you would have to pump up your air bags a lot. What this does is prevent your suspension from working properly (compressing) and transfers vibrations to next weak point ( coil retainer plate and chassis).
I have seen couple of vehicles with this kind of damage and i can tell you it can be severe. Answer is to install new coils properly rated for the load you WILL carry on your trip. Poly Air bags or similar products are NOT appropriate for off road use as they can render your suspension useless.This is especially pronounced on new Nissan models as their chassis and coil mounts are very THIN. Consider yourself warned and go and get in touch with some of the tour operators for right info about this product and it's intended use.

Goran, I am a bit confused when you say;

"What this does is prevent your suspension from working properly (compressing) and transfers vibrations to next weak point ( coil retainer plate and chassis)."

If one upgrades the steel springs, the load is transferred to the coil retainer and chassis. The heavier steel spring simply requires more force to compress it.

If one uses airbags instead, the load is still transferred to the coil retainer and chassis as force is still required to compress the air in the airbag, plus the existing "light" spring.

Either way, one simply has either a heavy spring OR a light spring + airbag. The additive effect of the light spring + airbag is equivalent to the heavy steel spring. In both instances the load is still transferred to the same point (coil retainer plate and chassis). There is no difference where the two transfer their load to.

It is a fact that airbags give a softer, more compliant ride than springs. Look at motorhomes, they upgrade to airbags to improve the ride (yet no change in their load capacity).

I suspect the damage you have seen has been caused by overloaded vehicles that have had the airbags pumped way up in an attempt to compensate for the load. If so, this type of damage would have occurred with either airbags or heavier springs.

Airbags do reduce offroad articulation, but so do heavier springs for the same load. At least airbags can be deflated to reduce their effect whereas heavier coils need to be replaced. It is the adjustability of airbags that attracts me. I have previously used heavy coils and they are not practical when varying the load significantly.

At the end of the day, an airbag is simply a type of spring, just not coiled steel.

Cheers

Mark

True. That is what you do with air bags. Inflate to copensate for the load. And it is so easy to overinflate to prevent bottoming out in the rough going. I am not an engeneer but i suggest you ask some of the tour operators about the rate of fairlure on this product and subsequent chassis damage when used off road. I will never use Polyair or any other coil helping device.Sunspension upgrade is only solution. Air bags are used from factory on busses and trucks but i am not aware of any that come out with air bag inside coil.

Motorhomes and vehicles that tow caravans are suited well for this product. Just don't expose them to harsh real off road conditions.

Hi Goran, I think you hit it on the head when you say the bags are overinflated to compensate for the load. Either a heavy duty steel spring or an airbag will cause failure if a vehicle is so overloaded. Any vehicle that is overloaded, be it with heavy steel springs or airbags, will have potential chassis failure problems.

I must disagree with you though on 1 point. A suspension upgrade (ie. steel spring) is not the only solution. I actually happen to be an engineer and there is no substantial difference between a heavy duty steel spring (say 300lb) and a standard duty steel spring (typical 150 lb) plus an airbag pumped up to an equivalent 150lb. This combines to a total of 300lb, the same as the heavy steel spring. As the load is still transferred to the same point, the vehicle does not know whether its an airbag or heavy spring.

Note there are differences in damping characteristics between an airbag and a steel spring, but that does not effect the example here, the spring compression rate is still the same.

Also a steel spring length can be altered to improve ground clearance for the same spring rate, thus there is more flexability to tailor height/load characteristics (but no ability to change that height/load characteristic, unlike changing the pressure in an airbag)

If an airbag is used on a leaf sprung vehicle, it now transferres the load to a different point on the chassis and is a totally different case to coil springs (a leaf spring air bag is located approximately in the middle of the leaf, with the load transferred onto the chassis directly above). Thus the chassis design will come into play and there are potential problems.

As for airbags not suited for off-road, apart from the potential for puntures or snagged air lines, there is no substantial performance difference. In fact, an airbag has one advantage, as the "spring rate" can be fine tuned for the load at the time, or to maximise ground clearance (at the expense of articulation).

Cheers

Mark

PS apologies to Salmon for the thread divergence.

Captain, did you ever tried not to overload the vehicle when you going on 3 weeks trip? This couple of 4x4's that sufered damage that i have seen where not overloaded.

Goran, I personally never overload my vehicle. As I usually tow my van, there is plenty of room/capacity for what I need.

But getting back to my point, there is effectively no difference between steel springs or airbags from the vehicles point of view. The damage the particular vehicles suffered you refer to would probably have resulted regardless of airbags or steel springs.

I totally agree that a vehicle should not be overloaded and also that some sort of compensation needs to be made for heavy than normal (but within manufacturers limit) loads. The point i am trying to make is that, while both have advantages and disadvantages, as far as the vehicle is concerned it cannot tell what is transferring the load to the chassis point.

If the chassis point fails, its because of excess "load" (either too fast on corrugations, too many corrugations, too much luggage, too hard on bumps etc...). The fact that its airbags or steel springs transferring the load is irrelevant. Note that shock absorbers (really dampeners) have a dramatic effect on corrugations, particuarly at certain frequencies when the actual load can be significantly magnified. Good shocks can minimise the damaging effect of corrugations, but thats another whole story...

I can understand you have a preference for steel springs, but that does not make airbags a poor choice. IMHO there are many advantages for airbags, particularly when the load varies, like vehicle empty for the work week and full for the weekend.

I have had heavy coils on my previous 80 series and while they were great when loaded, they were too firm when unloaded. Airbags would have enabled a softer ride during the week. I respect your opinion, but still plan to use airbags so I can easily change the ride to suit my load. And i will probably add lifted coils down the track for improved ground clearance.

Cheers

Mark

I would have thought that airbag must add far more stress to the coil towers as the force required to compress the air in the bag increases exponentially i.e. it will require a massive force to compress the bag thru the last inch of travel before the axle hits the bump stop. Without polyairs the coil will absorb the compression force at a constant rate until the remaining stress is transferred from the coil towers to the bump stops.

Hi Micheal,

An airbag or steel spring, it makes no difference. When the force (bump) is applied to the axle/wheel, it is transferred by the "spring" to the chassis. The spring is compressed, but the load is still transferred to the chassis, the spring just stops it being a shock loading.

Physics say energy (force) cannot be destroyed, so where does it go? Most is used in lifting the car up (the "bump" you feel in your seat) and the chassis absorbs some of the load (vibration, movement etc...) and the shock absorber also "absorbs" some energy (that is why a shock get so hot on corrugated roads).

When a car travels a lot on corrugated loads, large forces are continuously transferred to the chassis, hence an oveloaded vehicle can easily suffer spring mount failure (or even a correctly loaded one that see's plenty of coruggated roads).

Having the correct springs is more about vehicle handling, control and occupant comfort than spring mount failure (excluding when the vehicle is so overloaded that it rests on the bump stops, or hits the bump stops regularly).

Cheers

Mark

PS: this is a simplistic explanation, but is overall accurate.

Don
Thank god someone finally got the question answered. You are spot on with the whole post. Took a while with a lot of info in between

Know offence macca, you could of answered his question if it bothered you that much !!!!!! Baz.

Sorry Baz.
I didnt mean to sound cynical, but I was about to answer the post and thought I had better read the threads before I do . I then came across Dons answer and it fitted the bill. Just my observations on how the thread went.

Mine for 100 series Landcruiser cost $180 Australian flown here from the U.S. when the dollar was around 55 Cents I think and only took five days to get here.
Andrew

John,
Can you email me on amac@bigpond.net.au re the set up on your mates Bitsarmissin. I have a challenger and would be interested to discuss his setup
Regards Allan Mc