How much pressure in air bag when towing ??

Submitted: Tuesday, May 06, 2014 at 23:21
ThreadID: 107652 Views:12338 Replies:8 FollowUps:11
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Have recently purchased old Land Cruiser with air bags as part of the rear suspension .Not sure what pressure is in them now but shortly taking off on our trip towing tandem Opal van , put the scales under the towball the other day when van was loaded and it was pretty spot on , 200 kg which is the required 10% of the aggregate ( 2000 ) . So any suggestions please what pressure when towing ??
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Reply By: Member - blackbird1937 - Wednesday, May 07, 2014 at 00:42

Wednesday, May 07, 2014 at 00:42
Hi Brian. I have new airbags in my Patrol. I have been told maximum pressure is 30 psi. My van is 2500 kg but have no idea what weight is on the tow ball. I have plenty of weight in the rear of patrol 240 litres of fuel, 60 litres of water, fridge, camping gear etc. I usually run 25 psi in the airbags. Have a good trip, but it is what you make it yourself.
AnswerID: 532013

Reply By: WBS - Wednesday, May 07, 2014 at 07:22

Wednesday, May 07, 2014 at 07:22
No matter what pressure you put in them, make sure you inflate them before you load your vehicle not after. If you read the instructions for Polyair bags that's what they say.

Start with the vehicle empty, , measure the distance of the top of the rear wheel arch to the ground, load the vehicle with what is a normal load for you, measure the distance again, unload, and inflate air bags, then re load your vehicle. If the wheel arch is the same distance from the ground as when unloaded you've got the right pressure. If not unload and apply more pressure to the air bag. Once you've got the vehicle level make sure you know what that pressure is, then you make sure you maintain that pressure in the airbags.

If you try to pump up the airbags when the vehicle is fully loaded you could blow the air lines or the connection between the airlines and the bags. Also, make sure there is some air in the airbags at all times when unloaded.

When loaded up for travel, I ran my Polyair airbags at 20PSI to suit my 80 Series but I did not include the weight of the towball when towing. I used a weight distribution hitch (WDH) to level the vehicle up when the caravan was attached. I'm not getting into any debates about the use of WDH's that's for you to decide.

WBS
AnswerID: 532023

Follow Up By: braggy - Wednesday, May 07, 2014 at 07:48

Wednesday, May 07, 2014 at 07:48
I do similar to WBS, but measure from arch to hub empty, then pump up to about 40psi (mine will take 80psi), load up and let air out till back to same height.
But i know now that 38psi is right for my rig.

Cheers Ken
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Follow Up By: Member - Tony H (touring oz) - Wednesday, May 07, 2014 at 07:58

Wednesday, May 07, 2014 at 07:58
Hi Brian,
Ken's airbags 'taking upto' 80 psi seems very high, but then he may have some wizz bang setup.
I would err on the side of caution as you dont know what brand they are & limit MAXIMUM pressure to 30psi (207kpa), & as mentioned else where, pump up when unloaded.
Insanity doesnt run in my family.... it gallops!

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Follow Up By: braggy - Wednesday, May 07, 2014 at 10:21

Wednesday, May 07, 2014 at 10:21
Made me think about that 80psi max,
so checked Thor airbags 10psi-150psi

Cheers Ken
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Follow Up By: Member - Serendipity(WA) - Wednesday, May 07, 2014 at 19:18

Wednesday, May 07, 2014 at 19:18
I have heard a lot of the air bags max is 30psi but mine are like Ken's air bags with recommended max of 150psi. I often run mine at 80psi when fully loaded. No problems now for 5 years and have just completed the CSR last year - probably over loaded in the start. No problems with the air bags.

Cheers

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Follow Up By: Member - Phil G (SA) - Wednesday, May 07, 2014 at 23:38

Wednesday, May 07, 2014 at 23:38
150psi is what the airbags will tolerate - not what you should run them at.
The airbags I've had (both leaf sprung and coil) are as solid as a rock at more than 30psi.
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Follow Up By: Member - Serendipity(WA) - Thursday, May 08, 2014 at 19:11

Thursday, May 08, 2014 at 19:11
Quite true Phil G - some brands are like that.

The ones I have purchased claimed to have pumped them up to 750psi just to see and then stopped as they felt is was a bit dangerous. That is an extreme test but works for me.

My compressor has a shut off switch rated at 135psi that came with the air bag kit. The ones I bought are Boss Airbags.
http://bossairsuspension.com.au/boss-airbags/

No affiliation just a satisfied customer after 5 years.

Cheers

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Follow Up By: Member - Phil G (SA) - Thursday, May 08, 2014 at 20:50

Thursday, May 08, 2014 at 20:50
I had the same Boss airbags on my 79series. I never needed/used more than 20 psi. Too much pressure in them means your suspension is no longer doing anything - just acting like a strut, which is why chassis get bent by having the airbag. Fortunately the Landcruiser chassis is stronger than most, but with 80psi, your tyres would be acting as the suspension.
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Follow Up By: Shaker - Saturday, May 10, 2014 at 21:45

Saturday, May 10, 2014 at 21:45
I think that spring insert air bags which only accept up to 35psi are getting mixed up with leaf spring bags that tolerate much higher pressures.
The best way to measure suspension height is from the underside of the wheel arch to the underside of the rim.
I have found 30psi in my insert air bags in the Prado perfect for towing our AORC Quantum, also used the same pressure towing our Vista RV Crossover.

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FollowupID: 815453

Reply By: Brian - Wednesday, May 07, 2014 at 07:41

Wednesday, May 07, 2014 at 07:41
Many thanks again , great site , great people
AnswerID: 532027

Reply By: Member - David Will (VIC) - Wednesday, May 07, 2014 at 09:30

Wednesday, May 07, 2014 at 09:30
Hi Brian,
Also if you use a bike pump to inflate the air bags you can do a lot better, as you only need small amounts of air to change pressure. That way you can do it in small amounts until you get it right.

David.
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AnswerID: 532037

Reply By: baz&pud (tassie) - Wednesday, May 07, 2014 at 19:25

Wednesday, May 07, 2014 at 19:25
Brian,
If the air bags are red, they could be Pedders ones, require a minimum of 5psi to a maximum of 30psi.
As suggested, pump up before loading, if vehicle not level, just release a SMALL amount of air out till you are at the required height.
Cheers.
baz
Go caravaning, life is so much shorter than death.

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AnswerID: 532068

Follow Up By: Alloy c/t - Saturday, May 10, 2014 at 14:55

Saturday, May 10, 2014 at 14:55
And if they are the Blue Firestones a min of 5psi to a max of 100psi but you would never need them that high..
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Follow Up By: Shaker - Sunday, May 11, 2014 at 20:34

Sunday, May 11, 2014 at 20:34
Firestone Coil Rite air bags are blue & have minimum of 5psi & a maximum of 30psi, certainly not 100psi!
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FollowupID: 815531

Reply By: Bludge - Thursday, May 08, 2014 at 10:16

Thursday, May 08, 2014 at 10:16
Brian,

I don't think that there is one pressure that fits all...

I was told that the best way to find what pressures your bags require is to hook up the fully loaded vehicle to the loaded van, normally the tail of the vehicle and front of the van drops.

Wind up the jockey wheel until the vehicle and van are at the required level, then using a foot pump or compressor, pump up the airbag on each side evenly until the jockey wheel becomes “light” just use the jockey wheel winder to check this.

Then check that the vehicle is level left to right (fuel tanks, fridges and loading can make left or right heavier that the other side. Wind up the jockey wheel and check what pressure is in each bag.

This will vary on every vehicle/van combination.
Before you hook up and when you go to fuel up before a trip, inflate the airbags to the known pressures, don’t forget to drop the pressures when unhooked.

Good luck.
TonyV

Cairns FNQ.

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AnswerID: 532097

Reply By: Brian - Saturday, May 10, 2014 at 01:14

Saturday, May 10, 2014 at 01:14
Well i started off by erring on the side of Caution by putting 25 psi in , made van very out of level (tilting towards the back ) so i drove for a while very cautiously and van began to Wobble , so stopped deflated bags a bit , van ride was a fair bit better but still dipping at the back , will check pressures tomorrow , might have to consider a WDH ?
AnswerID: 532199

Follow Up By: Batt's - Monday, May 12, 2014 at 00:47

Monday, May 12, 2014 at 00:47
If the van is loaded correctly and you have weight on the tow ball but not exceeding the max somewhere around 1/2 to 3/4 of the max is ideal and the rear of the van is lower than the front then a WDH is not the answer. You need to get the van riding level to make it safe so you may need to buy a towing hitch that lowers the tow ball which is the usually solution. If you are going to be driving off road you can raise the suspension on the van to suit or fit larger tyres.
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FollowupID: 815545

Reply By: Brian - Thursday, May 15, 2014 at 01:10

Thursday, May 15, 2014 at 01:10
Thanks Batt , found that i could reverse my tow ball , undid split pin ,knocked out main pin and took out tow bar square shaft and took ball off reversed the shaft put ball back on which meant my tow ball is aprox 4 inches lower, ride is great now , thank you every one again
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