Air bag pressures on corrugations

Hi Hoyks,
have you any first hand experience with lowering in coil air bag pressures over corrugations? If so, what pressures did you run and what was the effect of running the lower pressures.

No, my experience is on bikes that would suck a tiny amount of air past the seals as the front forks moved through their stroke.
After a bit of hard riding over rough ground the forks would become quite stiff and jarring when hitting lumps, so you'd stop, vent the pressure through the valve provided and carry on.

I've heard of some running upwards of 50psi in the bags, which to my way of thinking would make them a bit on the firm side, more like rigid.

Thanks Batts,
I guess I'll just have to experiment, Was hoping for some definitive information from someone who has already done the experimentation over corrugations.

So have you tried lowering the pressures in your air bags over corrugations?

No I haven't as the airbags are there to maintain ride height and prevent the suspension and vehicle bottoming out. If your going to lower the pressures you may as well not fit them.

The load on a shock is only created by the end being fixed and the shock moving at speed to cause internal fluid to resist the movement. It heats the shock fluid as "work" is being done on the fluid, similar to hydraulic systems.
Lowering suspension bag pressure will reduce the speed of rebound.
The speed at which the suspension hits the corrugation is the bit which loads a shock absorber. If lower speed of compression and controlled, ie lower tyre pressures ( the initial/primary suspension system on any vehicle) then the shock is suffering less heat loading. Slower road speed means there is more time for the shock heat to be dissipated. Fast means repetitive/constant heat input to destroy the shock.

If you lower the air bag pressure the car will drop under the load till the spring and new airbag pressure supports the same amount of weight as was being supported before you lowered the pressure, ie the spring is taking more of the load the airbag less. Therefore it would depend on the spring rate compared to the airbag rate, if the spring rate is higher then the speed of rebound might actually be higher with the airbag lower, vice versa if the air bag rate is higher, if they are the same then no change.

HKB Electronics . With air bags fitted the air bag will be absorbing some or all of this energy and transferring it to chassis in a more controlled manor.
-------------------------------------------------------------------

That may not be true. A point that is often overlooked with air bags is they are exponential springs, not linear springs like the originals in the car. The more you compress them the more they resist further compression. Bump rubbers do the same thing. They have to because they must stop the chassis hitting the axle so they compress softly at first then harden up rapidly if the downward force on them is high enough.

Linear springs just keep compressing in proportion to the load. If you double the load you double the compression. If the car comes down hard enough on them to reach the bump rubbers, the rubbers take over and bring it to a sudden but slightly cushioned stop within the short distance they have to work in.

Installing an air bag is like installing an oversize bump rubber. They can be like a rock by the time they are around 70% compressed. They can and have done a lot of damaged to chassis, axle housings and wheel studs when you place an excessive load in the rear then throw in a dirt road and a bit of speed.

The impact forces going up into a car increase by the square of the speed when it goes through a dip or hits a high spot in the road.

Some cars survive and some don't.

Granted:

What I wrote was referring to installing an airbag for ride levelling under reasonable circumstances, not a grossly overloaded vehicle.

A lot cars these days have progress spring rates, ie similar to airbags, some caravan and trucks only have airbags but of course they have been designed for this.

"They can and have done a lot of damaged to chassis, axle housings and wheel studs when you place an excessive load in the rear then throw in a dirt road and a bit of speed."

I imagine they can in a grossly overloaded vehicle, but looking at it logically we have an airbag spring combo supporting the load, Upward movement is sufficient to compress the air bag to the point where it damages the chassis that's even with the progressive dampening affect. We now replace the air bag spring combo with just a spring that can support the same weight, we again apply the same upward force, As you wrote springs are linear, when apply upward force to the spring airbag combo, the airbag progressively applies more resistance to the travel ie it spreads the impact over the suspension travel, but still ends up damaging the chassis. We now replace the combo with a spring, the spring is linear so does not progressively impede the travel the suspension moves up at a much higher speed and slams into the bump stop which has to absorb the impact, I wonder what damage this would do?

It is easy to look at suspension and chassis damage etc and say oh look the airbag caused that, it would be interesting replace the air bag spring combo with just springs capable of supporting the same excess load and redo the exact same scenario above and see how well the vehicles faired? The problem is not the airbag, the problem was the car was overload to start with.

I know in my car the airbag pressure are certainly nowhere near high enough to stop the rear axle hitting the bump stops. I would be interesting to see just how much load and pressure in the airbag would be required to get the airbag to a point where it would prevent the axle hitting the bump stop?

What I wrote was referring to installing an airbag for ride levelling under reasonable circumstances, not a grossly overloaded vehicle
---------------------------------------------------------------

A correctly loaded car will not need leveling, it will sit at exactly at the height its manufacturer intended. I have had my ute loaded to the maximum and with two people in it, it was right on maximum weight according to a weighbridge at One Steel Metal Recyclers. It was not exactly level though, it still had a slight down hill slope to the front not the rear.

The big difference here was the load consisted of hundreds of small items that belonged to a charity. That made it very easy to distribute the weight correctly. I did not know its weight at home but I could see it had a forward rake and plenty of clearance between the rear axle and the bump rubbers.

It is weight distribution that brings many 4x4 owners unstuck. They can't always get everything in the right place and the most common result is the rear is overloaded and sagging and there is too little weight on the front wheels.

Loading correctly or getting a bigger car is the answer, not changing the suspension design. Apart from the damage that has been caused to many cars by overloaded rear ends, all that weight on the rear and stiffened rear suspension will almost certainly change the handling characteristics. Instead of understeering like the manufacturer intended, it will most likely oversteer. I would not be surprised if that has been a contributing factor in the large number of roll overs on dirt roads.

The other is the brake pressure is usually increased automatically at the rear when it goes down under load. Lifting it back up again will reduce the pressure. You now have a heavily loaded car at the rear with the brakes set as though it was empty.

Then there is the changes lifting it at the rear has done to the roll understeer feature of the original design.

You could go on all day talking about what these changes have done when you take the time to study how the whole thing has been designed. There is a hell of a lot more to it than meets the eye.

"Loading correctly or getting a bigger car is the answer"

Sounds good but then there's going to be a lot of caravan owners ok there using weight distribution hitches etc that will need to change their cars if simple ride leveling is the issue.

Then we get into the what car are you going to buy, you have mentioned your car is correct GVM on the weigh bridge therefore is legal. My Prado came from the dealer fitted with OEM bull bar and winch. When I put it on a weigh bridge the front axle was already over the max loading with two occupants in the car, if I was to fill both tanks and put bums on seats it would probably be over its GVM limit. The fact that the car is under its weight limit doesn't mean all the axle loadings are, or that it will be level at the height the designer settled on. With the Prado empty ie from the dealer attaching the camper and applying its 120Kg to the dealer fitted, OEM tow bar well under the max ball weight causes the back to drop, it certainly isn't overloaded in that instant. You then fill the tanks with 180ltrs and it drops more, with two in the front and still under its max weight it is tail down now if you only travel on the black stuff and your not worried about the car being down at the back camper being down at the front then you maybe happy with this. In our case the roads we travel you need all the ground clearance you can get, hence why there are things such as airbags and weight distribution hitches and after market suspensions which are all road legal if you remain with the specified standards. In my case the rear braking is loads are done by ABS, there is no height sensors in the rear so load proportioning based on road height is not an issue.

Again in my Prado, the after market suspension improved the handling of the car dramatically, before the suspension upgrade it rolled and wallowed around and had a lot of under steer as you mentioned. After the upgrade the rolling was reduced considerably and the car steers much better. There's nothing wrong with an upgraded suspension, it is those that think now I can load with anything I want and go as fast as I want that are the problem. I have never seen anyone who has broken a chassis or suspension, sheared of wheel studs on a car or trailer with or without airbags fitted say, it was my fault, I was going to fast and or had to much load on board, it is always the airbags or faulty after market suspension that are the problem and putting to much stress on points that weren't designed for the load, it not the two tons of gear I have in the car or the fact I was going flat chat to cover as much distance as I can!

I remember on our last trip, three 4X4's coming from the opposite direction and and listening to the chatter on the CB about the corrigations and the bull dust and how much fun they were having, I was doing about 70KMH and I thought that was pushing the limits, I gave them a shout letting them know there was a vehicle heading towards them, the first of the group still came around a corner sideways on our side of the road at easily over 100KMH in deep bull dust ruts, if I hadn't stopped he would have collected us. The cars where fully loaded both inside and on the roof racks.

The other main issue I see these days is car and van manufactures putting vehicles on the road that have little carrying capacity that are targeted to those they know will be loading them up, some of these vehicles are already overloaded with just full tanks and bums on seats, rather the authorities fine drivers and van owners, they should be chasing the manufacturers when vehicles have unrealistic weight limits and are not obvious overloaded by the owners, but then it is easier to fine the driver who is probably not even aware the car is overloaded than chase the manufacturer.

From what I have seen in the outback the main contributor to roll overs, broken vehicles and trailers etc is the actions of the persons driving them.

Yes your right there's more to it than meets the eye.

My Prado came from the dealer fitted with OEM bull bar and winch. When I put it on a weigh bridge the front axle was already over the max loading with two occupants in the car,
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,

That is common with many cars. If the bull bar and winch was fitted on Toyota's assembly line then the car would have had heavier springs installed at the front and most likely a few other alterations to the suspension to cater for the additional weight and change in its handling characteristics.

About a month ago I read a review on a soon to be released Hilux 4x4 that I think will be called a "Rugged". It has a factory fitted bull bar and stiffer front springs to cater for the additional weight which is not only on the front but is hanging about half a metre in front of the centre line of the wheels. The leverage would have added even more weight to the front suspension.

That is normal procedure for car makers. They don't just throw an extra 80 to 100 kilos on the front and leave it at that. If you go back to the days when factory fitted air conditioning was an option, you would find front springs listed in the dealer's parts book for cars that rolled off the assembly line with air and a different part number spring for those without it.

If the dealer installed the air conditioning kit, the car would not have the stiffer springs. This is what happens when you get a dealer or aftermarket company to fit a bull bar and winch. I know because I have installed both bull bars and air conditioning kits while working for new car dealers in my younger days.

The suspension has not been designed for these accessories and the front end will most likely be over its maximum axle capacity.

That additional weight on your front end that took it over its maximum capacity would have also caused the increase in understeer that you noticed. You can't alter anything on a car without affecting something else.

,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
The other main issue I see these days is car and van manufactures putting vehicles on the road that have little carrying capacity that are targeted to those they know will be loading them up, some of these vehicles are already overloaded with just full tanks and bums on seats,
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,

There is only so much carrying capacity that can go into cars like Prados, Landcruisers etc. unless you build them like mini trucks with dual rear wheels and a very hard suspension. Sales would fall through the floor if they did that.

The big mistake so many people make is they don't understand that a car like my single cab ute has its main load carrying area out the back in the tray while station wagon or SUV designs have their maximum load carrying area in the seats.

Look at the average weight of people these days.WEIGHT Add winter clothes and it would be up over 90 kilos for men and many are well above that. That is what car designers in this country have to contend with. They can't design the seats and weight distribution to cater for people the size of jockeys and no more.

This means all the popular five seat.cars like Prados and dual cab utes need over 450 kilos on the seats if the owner wants to load the car to its GVM. If you back off with seat weight and load up the rear end or tow ball, the car is going to be outside its design limits and sagging badly at the rear.

The aftermarket loves this and has a product to fix everything. Unfortunately when you alter the original suspension design, you gain something and loose something. The car can easily have some very undesirably handling traits that may not show up until it gets into an emergency situation and that could end in disaster if the driver can't handle it. .

By the way, when I had my single cab ute up to its maximum capacity, it did have a full load in the front. My wife and I weigh around the same weight and combined we are 150 kgs. Inside the cabin with us both behind and under the seat is a large recovery kit,. fire extinguisher, jack plate, UHF radio, an old but updated and heavy Barret 250 HF radio, a few tools including a tension wrench and some tyre inflating items to go with the ARB compressor under the bonnet. Then there is her handbag! It has no bull bar.

That would have taken the cabin load up to its maximum of around 200 kgs .

We agree with the speed issue ,we have coil springs in an 80 series with air bags and a 2" lift.
We let the tyres down for corrugations but not the air bags.
We drive to the conditions.
Going up to Cape York is a good experience, the speeds traveled at & the damage seen done to vehicles is terrible on the development Road.
Take care,Safe travels. Ma.

You let out 10 PSI, how much weight are you carrying, I have heavily loaded rear draws, cargo barriers etc, 120K ball weight of the camper and inflate mine to 6PSI to level the car with the camper attached?

Considering it takes about half a second to dump 10 psi and about 3 seconds to shove 35 Psi in I'm struggling to think how you are able to get 6psi ?
Airbags are rated to 100 psi and as I stated they are on a much heavier vehicle than a Prado
Sure you have heavy drawers and 120 kg tow ball weight, but as I have said each vehicle is different in many ways.
If you run 6 psi good onya, but as you have stated below "under pressure" appears can be detrimental.
Dingoblue has asked a simple question and received many answers to satisfy his curiosity and his vehicle is totally different to my vehicle and yours, and as I stated I have spent time experimenting this and found it effective for my needs thank you

Flighty,

I was just curious to know how much weight you are carrying, yes getting around 6PSI can be fiddly, and yes running to low a pressure can damage the airbag, minimum air pressure for mine is 5PSI, 6PSI brings it back to the standard ride height.

As you can see from profile pic I have the canopy on and two 285/75 tyres and rims hanging off the back.
and canopy is 2 mm aluminium and not 3mm as most manufacturers construct them with.
RTT ( fitted 12 m ago) is 80 kg on top and 80 litres of water underneath but located at front of tray, inside is a rather large tool box and fridges etc with all the usual garbage that one tends to carry on extended trips

Rear springs are 600 kg constant load and vehicle sits level without airbags and 35 psi raises it by approx. 20 mm only

All up with 2 full tanks of fuel and water tank full I am approx. 3300 kg
bearing in mind that kerb weight is 2014 kg (including fuel)

My Prado is 3160 kg fully loaded:(

6psi it really wouldn't be worth having air bags at that low a pressure the amount of money you paid for them you could have moved something in the vehicle or camper and made a bigger difference for free. Also if you left them at 5psi they would come up higher than 6psi with the heat generated from running.

Have raised normal springs in the in the rear, without the air bags the 120 kilos or so of the camper plus the load in the rear storage cause the back to drop, 6PSI or so levels it up again. Other alternative was raised heavy duty springs but they make the rear ride a lot harsher. With the raised normal springs and the airbags the ride is better than the OEM setup.

Lowering the tow ball weight is a not on, I don't really want to move everything out of the back forward of the rear axle, the front axle is already over its rated load with the bulbar and winch.

Temperature wise, haven't every measured the temperature of the airbags but I don't image it would rise that much, not like a tyre carry large loads and rotating, compression would cause the air temperature to rise but then it expands and cools again.

All answers appear to mean well and meant to assist in some way, none was off topic or far fetched
All good

You asked do people lower the airbag pressures, and asked for experience from persons who are using them.

I do use them and no I don't lower the pressures, I believe that answered question, I have had no need to as the ride is fine just lowering the tyre pressures, what would have been more helpful is if you indicated how much load you are carrying and how much pressure your putting in the airbag, as one pointed out above who does lower his pressure is he lowers his 10psi, I only need to inflate mine to 6PSI to level the vehicle. Lowering the pressures on the above vehicle improve the ride, if I was to do the same it may worsen the ride, it would depend on the vehicles spring rate compared to that of the airbag rate.

Airbags are used to raise the height of the vehicle to what it was before it was loaded as such there is no defined pressure for the airbag, so if you need to smooth the ride then it may help, suck it and see but be aware it lowering the pressures may also affect the handling of the vehicle and cause possible damage to the airbag and or suspension.

DingoBlue
Because you asked for some info but gave little indication as to the extent of your personal experience or understanding of suspension, people attempt to fill in the gaps they see may be there, in order for you to be more informed.
Yes, many people have different experiences, some useage practical, and some technical experience, unless they know your starting point they don't really know exactly what to tell you.
Just saying, "yes we lower the airbag pressure", may not help you and to be aware of associated factors is not a bad idea.
That way you can make a more informed final decision. Simply getting an answer to your question, what you want, when you want it may not be in your best interest.
I endorse the various comments so many possible issues are covered.
Would you just prefer 'YES/NO"?

You said you had rear coils with airbags, Flighty has leaf springs 2 totally different configurations, so how does that help you?

I might add im running AT BFG's 265/70/17 and CSA steel rims all new sets at the start of trip.

Cruiser .
Great to see there are still travellers who use common sense .
Well written .

Cheers