Poly air

Submitted: Thursday, Mar 11, 2004 at 19:36
ThreadID: 11179 Views:3463 Replies:10 FollowUps:17
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I have the latest Nissan Patrol Cab/Chassis with coil springs. Towing a 20 ft. van with about 275kg. drawbar weight. Will be using a Hayman reece weight distribution kit to even it all out. Would it help or would it be an over kill to also put in poly airs.
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Reply By: Wayne (NSW) - Thursday, Mar 11, 2004 at 19:45

Thursday, Mar 11, 2004 at 19:45
Salmon,

The Hayman Reece weight distribution hitch whould be better because it not only evans the weight, but also help to stabilize the vehicle and van. This unit however would not be good off road, regaurdless of the size of the van.

Wayne
AnswerID: 49978

Follow Up By: Baz (NSW) - Thursday, Mar 11, 2004 at 20:16

Thursday, Mar 11, 2004 at 20:16
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 ?
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Follow Up By: Wayne (NSW) - Thursday, Mar 11, 2004 at 20:27

Thursday, Mar 11, 2004 at 20:27
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.
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Reply By: Member - Raymond - Thursday, Mar 11, 2004 at 20:39

Thursday, Mar 11, 2004 at 20:39
Hi Salmon
I have the coilcab with a slideon camper. The Polyiars have been fitted for over 12 months and they have been great. They have improved the ride and also allow me to alter the ride for when the camper is off and more importantly when "she who must be obeyed" get to see how much she can load in one camper.
Ray
AnswerID: 49992

Follow Up By: Baz (NSW) - Thursday, Mar 11, 2004 at 21:41

Thursday, Mar 11, 2004 at 21:41
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.
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Reply By: Crackles - Thursday, Mar 11, 2004 at 22:08

Thursday, Mar 11, 2004 at 22:08
If the Hayman Reece kit won't level it out you certainly have too much on the ball and would need to redistribute some weight in the van. I don't pump my Polyairs up much when towing with level riders as their doesn't seem to be any need however they are great for towing without them or for carrying all the gear that 4 girls seem to pack in the rear. Polyair bags are really just a temporary solution. It is always better to have the correct rated springs to carry the load. For the same price of the bags you can get a pair of firmer springs to do the job. Craig............
AnswerID: 50007

Reply By: Member - Andrew(WA) - Thursday, Mar 11, 2004 at 22:30

Thursday, Mar 11, 2004 at 22:30
Salmon

I recently towed a van around the country with 3 kids in the back seat and the back of the GU patrol loaded to the roof. I installed Poly Airs before I went and apart from the Engel..they were the best money spent.

They level the car very effectively and stop the rear end bottoming out over railway crossings, cattle grids etc etc.

They will definately help but if you have the quids..I'd explore the cost effectiveness of a suspension upgarde. I understand this will give even better performance all round. I still have standard set up but will look at upgrading in the future.
AnswerID: 50014

Reply By: Rowler - Thursday, Mar 11, 2004 at 23:07

Thursday, Mar 11, 2004 at 23:07
Salmon, you might want to do a search on GU patrol rear coil caps (tops) bending upwards, some people have had it happen & I have reinforced mine prior to loading up for the big trip.

Cheers Rowler (dave)
AnswerID: 50027

Reply By: Member - Captain (WA) - Thursday, Mar 11, 2004 at 23:30

Thursday, Mar 11, 2004 at 23:30
I tow on my van on a regular basis and currently only have standard suspension on the GU Patrol. However, I intend to install airbags to help when fully loaded. I do not intend to upgrade the rear suspension as I often have no load.

On my previous 80 series I had 300lb Kings coils in the rear and they were great when towing. However, on a day to day basis they were too firm when unloaded. As my patrol will be doing a similair mix of being loaded and unloaded, the planned polyairs will give the option of varying the "spring" rate, unlike a permanent spring upgrade.

But if you will always have a large load, then the spring upgrade is a more cost effective option. If the cost is not an overiding factor, I prefer the polyairs as it is adjustable for the load at the time.

As for the polyairs being over kill, hmmm... may not strictly be required, but is better IMHO to balance the load with the springs/airbags and then use the weight distribution hitch for fine tuning of the handling. When towing something of that weight, I do not think one can go overboard on balancing the vehicle.

I personally shy away from the weight distribution hitch as they really limit off-road clearance. Do not know if this is a factor for you, but if towing off-road (not just gravel) then its something to consider.

Cheers

Mark
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Follow Up By: Goran - Friday, Mar 12, 2004 at 12:17

Friday, Mar 12, 2004 at 12:17
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.
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Follow Up By: Member - Captain (WA) - Friday, Mar 12, 2004 at 13:03

Friday, Mar 12, 2004 at 13:03
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
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Follow Up By: Goran - Friday, Mar 12, 2004 at 13:28

Friday, Mar 12, 2004 at 13:28
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.
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Follow Up By: Goran - Friday, Mar 12, 2004 at 13:34

Friday, Mar 12, 2004 at 13:34
Motorhomes and vehicles that tow caravans are suited well for this product. Just don't expose them to harsh real off road conditions.
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Follow Up By: Member - Captain (WA) - Friday, Mar 12, 2004 at 15:04

Friday, Mar 12, 2004 at 15:04
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.
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Follow Up By: Goran - Friday, Mar 12, 2004 at 18:57

Friday, Mar 12, 2004 at 18:57
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.
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Follow Up By: Member - Captain (WA) - Friday, Mar 12, 2004 at 21:34

Friday, Mar 12, 2004 at 21:34
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
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Follow Up By: Michael_FNQ - Friday, Mar 12, 2004 at 23:14

Friday, Mar 12, 2004 at 23:14
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.
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Follow Up By: Member - Captain (WA) - Friday, Mar 12, 2004 at 23:45

Friday, Mar 12, 2004 at 23:45
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.
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Reply By: donk - Friday, Mar 12, 2004 at 00:32

Friday, Mar 12, 2004 at 00:32
Salmon

I tend to look at it this way

The van should be attached to a level vehicle

If the vehicle is not level (low at the rear) before the van is attached than you need to modify the suspension with heavier springs,polyairs,ect.

The weight distributing hitch is used to return the vehicle to level after the van is attached (compensate for the ball weight of the van only)

Regards Don
AnswerID: 50035

Follow Up By: macca - Friday, Mar 12, 2004 at 07:12

Friday, Mar 12, 2004 at 07:12
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
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FollowupID: 311840

Follow Up By: Baz (NSW) - Friday, Mar 12, 2004 at 11:06

Friday, Mar 12, 2004 at 11:06
Know offence macca, you could of answered his question if it bothered you that much !!!!!! Baz.
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FollowupID: 311861

Follow Up By: macca - Friday, Mar 12, 2004 at 12:38

Friday, Mar 12, 2004 at 12:38
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.
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FollowupID: 311873

Reply By: Member - Bob - Friday, Mar 12, 2004 at 07:36

Friday, Mar 12, 2004 at 07:36
How much have people spent on Poly Airs? For the occasional big load they seem a better option than swapping springs every time you load up or down.
AnswerID: 50042

Reply By: MrBitchi - Friday, Mar 12, 2004 at 09:24

Friday, Mar 12, 2004 at 09:24
You might want to have a look at this mob. Fraction of the cost of local suppliers and ship in around 5 days. Co-worker just got a set for his Challenger no problems.

http://www.truckspring.com

John
AnswerID: 50052

Follow Up By: Member - Andrew & Jen (Melb) - Friday, Mar 12, 2004 at 11:18

Friday, Mar 12, 2004 at 11:18
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
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FollowupID: 311863

Follow Up By: macca - Monday, Mar 15, 2004 at 22:47

Monday, Mar 15, 2004 at 22:47
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
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FollowupID: 312261

Reply By: Member - JohnR (Vic) - Saturday, Mar 13, 2004 at 15:04

Saturday, Mar 13, 2004 at 15:04
Salmon, I think that Captain is pretty right in what he says about the shocks to our vehicles from corrugations. A combination of speed, weight and consistent pounding of the components has caused problems in GU suspension towers. I do think the area is under engineered for some of the cab/chassis combinations. They are not made to carry the tonne we may think they should for such a big truck.

I have a plate mounted over the top of my spring towers of the 2003 model I have. I had bent them up in the first 13k Kms we had done with standard springs and Ployairs. I would have thought a weight like that well behind the rear axle has the same capacity as any overloading and shocks into the chassis. Just remembering how far forward the GU axle is on the cab/chassis.

Go for Polyairs but watch your spring mounts as you will undoutedly put some extra on the tray and get the shocks transferred into the chassis or spring towers
Cheers,
Who?
John

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AnswerID: 50185

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