Tyre and airbag pressure

Submitted: Sunday, Mar 23, 2014 at 01:59
ThreadID: 106846 Views:1797 Replies:6 FollowUps:3
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Hi guys
I have a landcruiser 200 series which has 285 /60 R 18 all terrain tyres. I run then on about 35 psi on normal roads. It has had a GVM upgrade so shockers and coil suspension

I am picking up an off road caravan next week. It will have the same tyres but will have air bag suspension

I am doing gibb river road in couple of months. Realise I need to lower tyre pressure being wary not to run on wall of tyres- I was thinking about 28 psi for starters

But what about airbag suspension - I can raise or lower this, I think the range is from 20 psi to about 80 psi. Don't know the brand as yet

Does anyone know much about this

Thanks
Rusty
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Reply By: MEMBER - Darian, SA - Sunday, Mar 23, 2014 at 08:16

Sunday, Mar 23, 2014 at 08:16
Our van has ind. air bag and shocker suspension. Advice from the manufacturer is that it needs to be fully up for any travel....normal movement of the arms could bottom out on the chassis otherwise and I'm told the bags are designed to be fully extended while working. We soften our 265/75 BFG tyres to 30 for gravel and the van and contents seem very happy with the ride. I'm sure others will comment on the 200 with 18's.
AnswerID: 528913

Follow Up By: Ross M - Sunday, Mar 23, 2014 at 09:53

Sunday, Mar 23, 2014 at 09:53
If the bags are FULLY extended while travelling that means the arms are at full down. Therefore, when road undulations are encountered or you go over a sudden drop off the wheel has no abiity to droop and maintain road contact.
If that happens with side winds, at corners or when sway is present then there is no grip of the trye and there would be a loss of control of the caravan.

Methinks the usual 1/3 ability of the suspension travel as droop still applies to a caravan.

Always question what you are told because usually the laws of physics don't change
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Follow Up By: MEMBER - Darian, SA - Sunday, Mar 23, 2014 at 12:23

Sunday, Mar 23, 2014 at 12:23
A clarification Ross - my description could have been more accurate.....the bags need to be extended to their 'design position' - that point is set by the adjustable pneumatic valves that control the system (one simply turns on the compressor and the hardware does the rest). From that point, up and down movement of the arms takes place. When camped, owners can release all or part of the air to lower the door step - individual sides can be lowered too, to level the van. The main thing I think is that having less than the design height/pressure when mobile risks suspension damage.
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Follow Up By: Ross M - Sunday, Mar 23, 2014 at 19:07

Sunday, Mar 23, 2014 at 19:07
That is what I thought it would be like. All good.
Do you use a settle ability to lower while stopped and setup?
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Reply By: Member Andys Adventures - Sunday, Mar 23, 2014 at 08:22

Sunday, Mar 23, 2014 at 08:22
Hi Rusty,
I run the same in the air bags as in the tyres. So on the open road it's 40psi on the dirt it's 28/30psi. Works for me but every car is different you will just have to try different settings along the way.
AnswerID: 528914

Reply By: The Bantam - Sunday, Mar 23, 2014 at 09:46

Sunday, Mar 23, 2014 at 09:46
Seeking advice from others concerning tyre pressure is a bit of a lottery.

In general YOU need to consider the load YOU are carrying and the tyres YOU have fitted.

First step is to obtain a load V pressure table for the tyres in question.(either from the manufacturer or from the tyre standards manual) ( every tyre shop should have a coppy of the standards manual)

The load V pressure data should be the same for any brand or tread pattern of a specific type & size tyre, because it is determined by carcase type and air volume

Then you should load the vehicle as it will travel including occupants and put it over a weigh bridge.
Make sure you get an axle split. ( some weigh bridges you will have to drive over and read the axles as they come on or go off..because they cant split axles on the bridge)

From that information you can determine the minimum highway inflation pressure required for each axle...this is your starting point.

This is the only reliable way to determine correct tyre pressure.

Almost certainly you should running different tyre pressures on different axles and those pressures will vary depending on what you have loaded.

As for pressure reduction off road..you should only reduce tyre pressure IF you are reducing speed and then a reduction bassed on the correct tyre pressure for the load carried at the time.

In my 4wd loaded to travel I run 30 PSI in the highway, because its pretty evenly loaded across the axles and that is 2 psi higher than it works out off the tables.
If I have the vehicle loaded for work, I carry more weight & I have up to 45PSI in the rears.

Traveling off road when I can reduce the speed below 80Kmh I reduce to 24PSI...if I am traveling over soft stuff like sand and I can reduce my speed below 60Kmh I will reduce to 18PSI..that has proven to work for me.


Lots of people have tried to tell me I should be running different pressures...becasue that is what they run.

The whole tyre pressure thing should be different for everybody, bassed on their load and tyres selected.

As for the airbags...well that will vary depending on how the trailer is loaded too...I am sure there will be a table for that......otherwise you should be inflating to keep a correct attitude of the trailer and keeping it's suspension in its correct travel range.

Again nobody can tell you unless they know your rig and how it is loaded.

cheers
AnswerID: 528919

Reply By: Bob Y. - Qld - Sunday, Mar 23, 2014 at 10:33

Sunday, Mar 23, 2014 at 10:33
Rusty,

What I know about air bags on caravans you fit in top left hand corner of a postage stamp.

But do know a little about air bags on trucks. The air pressure in them is governed by a valve, and an arm off the rear axle. When unloaded, the valve provides just enough air pressure to keep the bag inflated, then as weight is applied, such as loading a trailer, then the truck lowers, the arm activates the valve and more pressure is applied to the bags. Too much pressure will burst the bags.

With the pressure range you've given, you might need to do some on road testing with empty van, then load it fully and increase pressures, to find best pressure range. Would suggest that to run, at say 80 psi constantly, would not only cause some handling issues, as highlighted by Ross, but may also eventually damage van, suspension and contents.

Hope to be on the Gibb in a few months too, enjoy the van,

Bob

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AnswerID: 528924

Reply By: Idler Chris - Sunday, Mar 23, 2014 at 13:37

Sunday, Mar 23, 2014 at 13:37
Tyres are a significant cost and are a safety issue if you do not get it near right. My solution which covers everyone's set up is this. Get reliable internal tyre monitors which tell you temperature and pressure. I do not like my tyres getting over 50 degrees so I set the pressure to achieve this no matter on the highway or off road. This takes in the main variables being load, speed, and ambient temperature. In really hot conditions I would also drive slower if necessary. You may not agree with 50 degrees and that is up to you, but this method tells you what is really happening so that you can make an informed decision as to pressure's and speed.
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Reply By: guy007 - Sunday, Mar 23, 2014 at 19:30

Sunday, Mar 23, 2014 at 19:30
Hi Rusty,
Did the Gibb last year. Van on 25psi with Simplicity suspension. Lc200 with GVM upgrade and Coilrite airbags at 15psi + 30psi rear and 28 psi front on 285/65/17 Bridgestones. Same trip the Plenty highway, Tanami and across the Top. No problems.
regards
Guy
AnswerID: 528945

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