Centralised Tyre Inflation System (CTIS)

Ultimark

Active member
Over the decades I’ve been travelling to various parts of our continent, and sometimes places overseas where one travels on dirt and muddy roads, not to mention sand, snow and other obstacles which has often meant that one compromises on the correct tyre pressure for the terrain, load and speed. For quite some time I have, like virtually everyone else, managed to adjust tyre pressures by stopping and airing down, then airing up with a portable compressor.

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I first I did this on motorcycles using a hand pump, which worked well, except when requiring pumping up in hot weather. One day I acquired a very small lightweight 12V pump for the motorcycle, by and large it worked; but it was slow.

Entering the four wheeled type of vehicle for travelling, I needed to up the compressor situation, pickings were slim, but they did manage the job. Another couple of decades and one had a 4x4 ute and a 12V portable compressor; this was heaven. But it still took quite some time to air down and air up, with the time taken to do this sometimes meaning that instead of airing down, one simply slowed right down for the 10-25km or so of dirt sections and felt the bumps quite a lot.

Military vehicles were pretty much the first to have a CTIS fitted to aid in traversing hard surfaces then to seamlessly switch to a different pressure for soft surfaces without requiring the driver to stop and air down. In a military sense having the vehicle stop to do this is not a good idea, so their usage was (I’m supposing) mainly driven by keeping their vehicle and driver(s) functional and alive.

Many people have heard of the German Unimog vehicle, which has as an extra, their own inbuilt CTIS. I’m not sure about early units, but their current offerings are linked directly to the vehicles computer system and will override if too low a setting has been set and the vehicle speed is increased by the operator over the tyre inflation parameters. MAN trucks also have a CTIS system as an option, but I’m not too sure if it is theirs or something they procure and build into their trucks. In Australia, as far as I know, these are the only two mainstream trucks that have a CTIS available ex-factory. For the rest of us, anything like this is an aftermarket possibility, albeit, a limited aftermarket possibility.

Large trucks run air brakes and therefore have a ready supply of compressed air which may be tapped and used for airing up tyres. Our truck, a January 2020 build Isuzu NPS 75-155 4x4 is a Light Rigid vehicle, which is any vehicle that has a GVM between 4.5 tonne and 8 tonne and only two axles in the Australian market. Our particular vehicle has a design build of 7.5 tonne and runs hydraulically operated drum brakes all round; I needed a compressor.

A few options are around with possibly the best option being a belt driven compressor driven straight from the engine; combine this with a tank and one is looking good. The belt driven compressor is fast, really fast, but the cost and modifications required along with COVID-19 everywhere and with the world shut down, it was not going to happen. Very expensive portable electrically powered heat pump style compressors were next on the list and except for non-availability due to COVID, I would have procured one.

I looked at ARB twin cylinder compressors, they were in short supply but ARB had something that would fit the bill, their 24V twin cylinder air compressor was in stock, complete with a tank in a portable carry case. Our truck has a 24V electrical system and for once, procuring an electrically driven accessory was easy. According to ARB their 24V twin cylinder air compressor has a 100% duty cycle and it certainly does a pretty good job of airing up the largish truck tyres.

This air compressor was used to manually air up the tyres for almost a year before we acquired our CTIS. Depending upon how low we had gone down, or how high up we were upping the tyre pressure, we could be waiting for about 12-15 minutes; which included unpacking and repacking the compressor stuff.

The decision to acquire a CTIS for the truck was driven by a few parameters. Firstly, the convenience. Secondly, the ability to maintain a constant air pressure, regardless of tyre temperature. Thirdly, the safety factor. An unexpected fourth parameter, was the comfort factor. There are only a few CTIS options available around the world, most of them are targeted to larger trucks and other heavy vehicles which already have an on-board compressor.

I started looking around the world.

Surprisingly, I found a manufacturer of a CTIS only 150km from home in Morwell, Victoria, Australia. AIR CTI is their name and they have been in business since 1999. This family business manufactures their CTIS in-house. One question I had was about the strength of the external hard pipe that is visible and sits outside of the tyres. I was assured that it was as strong as anything and I would be welcome to come to their factory and hammer a piece of their hard pipe on a steel bench with a steel hammer. I never did get to hammer the hard pipe, it got forgotten about in the discussions.

Their hard pipe material, which is the rigid part that is quite visible, is sourced in Australia and bent and manufactured at their factory. After doing some quite tight 4WD tracks that really hadn’t seen much use due to COVID and were therefore quite overgrown, the scariest part was listening to the vegetation make train tracks down each side of the truck and watching the hard pipes disappear into the shrubbery.

On the driver’s side we have two 140 litre fuel tanks, they are inboard of the wheels and at the same height as the hard pipes of the CTIS. Those fuel tanks now have some quite decent train lines running horizontally and the hard pipes have zero scratches. So for stuff that rubs really hard on the hard pipes, that hasn’t be an issue.

If something hooks the pipe that would be another issue. To that end AIR CTI gave us a length of spare soft pipe, which is the small section that connects the hard pipe to the rotator. The rotator is the small plastic bit in the very centre of the wheel which stays stationary while the wheel rotates. It maintains the air seal between the stationary part of the system and the rotating part. The design life of the rotator and its seals is 1,000,000 kilometres.

Their main market is trucks, but they also make a version for a normal car or ute based 4x4 vehicle or standard 2WD vehicle. From what I could physically see when walking around their facility, we could have one of their CTIS fitted to our bog standard Hyundai i30.
 

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Ultimark

Active member
In December 2021 I visited their factory to ascertain the viability of fitting a CTIS to the front wheels of our truck. Our truck has been modified by All Terrain Warriors in Qld with, among other things, a complete suspension change. The steering wheels have a 600mm arc of articulation and with the fitment of larger and wider super single tyres, the room for CTIS equipment that is also needed was probably going to be a tight fit. Although I thought it may be a big ask, it was doable. At the same time AIR CTI concluded that they would be able to adapt our portable ARB compressor to the truck for their CTIS.

Subsequently AIR CTI in Morwell did the whole conversion in their factory, although I could have purchased the componentry and either done it myself, or hire someone to do it. Being in the fortunate position of having AIR CTI just down the road, they did the conversion.

The CTIS has been fitted for almost a year and from the get go, it has been wonderful. The system has three pre-set pressures available, our system has been set to these parameters: Programme 1 is highway mode, Programme 2 is dirt roads with mild corrugations, Programme 3 is for low speed heavy sand, mud, snow etc. You can set each programme to any designated pressure that is applicable to your vehicle, and its requirements.

When one fires up the engine, the dashboard control starts and defaults to the highway mode; which has the highest pressures. When AIR CTI are setting the parameters, they require actual axle loads taken from a weighbridge and using the tyre ratings from the walls of the tyres fitted to the vehicle, they work out the pre-settings which are fed to the controller.

In use, the system is quite flexible. Our system is divided into two sections, the front steering axle and the rear drive axle. There isn’t a great difference in the load of each axle, so the tyre pressure difference isn’t that great. The percentage difference between the two axles as we change through P1 to P2 or P3, remains constant.

Once we are in a programme, we can individually raise or lower each axle individually by simply pressing an up or down arrow button. This helps us greatly in keeping the truck in trim. As the weight changes as we drive, we can and do change the pressures on each axle with careful trimming.

Using weighbridges as our reference, we have measured a weight change from refuelling and filling up the water tanks, for a collective 460 kg loss across both axles from fuel and water usage. We have 280 litres of fuel and 240 litres of water, and from full to near empty the dynamics of the truck do change.

The CTIS controller switches on when the engine starts, but I need to manually press the added compressor button on the dashboard to fire up the compressor. The compressor is left on all day, meaning that for the rest of the day whenever we start the truck the CTIS controller is ready to add air or deflate the tyres with the compressor kicking in automatically.

The controller readings in the picture are, left to right: actual measurement on the front axle of 330 kPa and on the right the setting pressure, which is 320 kPa. The difference is that there is a plus/minus factor of 1psi to 2psi . The software was designed using psi as the standard, but one can request to have either psi or kPa as the readout. We have kPa as our readout. As we drive along, one only has to press the up or down button to alter the highlighted axle for minor trimming changes; the picture is showing the front axle being the highlighted axle. The bottom line is the rear axle readout.

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The compressor is mounted on 5mm aluminium sheet which in turn is mounted on a wall in our storage box. AIR CTI retained the ARB hose coupling so we can still use the ARB 6m hose.

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The compressor supplies air to the ARB tank which has been mounted on a chassis rail under the tray.

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On the other side of the air tank, is the water filter and other stuff.

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From there the next stage is one of the two isolators, one for the front and one for the rear axle. The short blue pipe is where the air is expelled when the system is deflating tyres.

CTI_001_IMG_20220112_114846.jpg


In use we have been surprised at how often the system adds and subtracts air from the tyres. In the morning when leaving, the system fires up and checks and adjusts air pressure. Every morning so far, the system has added air as the tyres have cooled down overnight and are slightly lower than the requested pressure.

Within a short space of driving time and dependent upon the weather, the rear axle will often deflate for a second or two as the air in the tyres has warmed up and expanded. A short while later, the front axle usually does the same.

Once onto highway speeds, the system settles down and hardly changes. Although one day after an hour or so on highway speeds and coming into metropolitan Melbourne with a cool change happening, with rain and cool conditions and reduced speed, the tyres cooled down and the system added a little bit of air as and when it was needed.

These changes are quick and unless we hear the compressor working, or we hear the little bip from the dashboard mounted controller telling us it is doing something, we have usually been unaware of these changes. Except initially, when our eyes and ears were glued to the controller screen; as it is for all new stuff.

Below you can see a red and a black tab, this is something that AIR CTI manufactured specifically for our truck to allow us to change the vehicle from free-wheeling front hubs, to engaged front hubs that allow 4WD.

Directly under the “T” in CTI, you can see the manual air input. This allows one to use any compressor to manually up the tyre pressure; an override if you like.

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The system requires all Schrader valves to be removed, which from what I have now experienced, allows for quicker input and output of air as the ARB compressor certainly adds air faster than before. If the tyre valves are left in, the system cannot work!

Even though we have only had the CTIS for almost a year, we both wouldn’t like to head out without one of these fitted to any vehicle we are in; it’s that good!

AIR CTI can be found at, aircti.com

This is a you tube clip on one of their systems fitted to a Toyota Prado 4x4 sedan vehicle.



I have also seen a similar system to the above Toyota Prado fitted to an F350 Ford ute.
 
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Ultimark

Active member
Nice write up...
Can you give a ballpark price on what this CTI system cost?

Going off their current price list issued in May 2022, and this is for a 4X4 Flat Guard Kit, Drive and Steer, you will be looking at $9,240.00 AUD plus GST.

This is for the componentry only, and does not include a compressor.

Flat guard refers to the type of mudguards that are fitted, which in our case are flat aluminium mudguards on our drive axle. Many trucks, especially on their rear double or triple drive axle set-ups, often have round plastic mudguards.

The system is reasonably smart, if we have a slow puncture and the pressure starts to drop, the system covers it. If this pressure drop persists, after a couple of times of this happening the system delivers a warning that you have an issue somewhere. We haven't had any pressure drops like that, hopefully we don't; but nice to know it's there.
 

SkiFreak

Crazy Person
As you have said, you have not had any issues, but a concern of mine would be changing or rotating a wheel.
Without any schrader valves in the stems of the wheel I would imagine that you have to deflated the tyre first, then you have to pump up a deflated tyre. I just see that as potentially being time consuming. Am I wrong?
How do you get the fixed pipe out of the way when removing the wheel?
 

Ultimark

Active member
I've done a couple of wheel rotations this year, having the CTIS fitted has made minimal difference to the overall rotation procedure.

First cab off the rank is to use a brake line clamp, had these for decades and they work perfectly. One clamps the air line, then you remove it from the rotator.

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Next one undoes the two top (or outside) locknut nuts to fully release the rotator.

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Then you simply rotate the entire rotator, which is attached to the hard pipe. In this case the drivers side front hooks up perfectly with the drivers door. I use an ocky strap to hold it there.

Wheel_Rotation_IMG_20221105_135559.jpg

Then the wheel can come off and you are left with the metal plate that has a groove on the rear to enable switching from free wheeling hubs, to locked hubs. It fell onto the ground moments after I took this picture.

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One of the interesting features, is their patent applied for name, of their hard pipes. ;)

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Another quirk of the company is their name, AIR CTI, translates as:- Air In Rubber Centralised Tyre Inflation.

Once you have a wheel off, the only issue is removing the small length of clamped hose from one wheel to another. My procedure is to quickly unscrew the hose, then using a long handled valve tool, I quickly insert a valve and tighten it up with the valve tool. There is certainly some air loss, but unless one fumbles badly and drops a Schrader valve, the air loss is minimal.

Air loss isn't an issue at all as once I have done all four wheels, I just fire the truck up then the tyre inflation system automatically kicks in and re-inflates all four tyres to the correct pressure. Because I have an aftermarket compressor, not an OEM inbuilt compressor, I have to throw the added dashboard switch, which makes the compressor work.
 

Ultimark

Active member
Dan, it is a bit on the pricey side, but the more you look into this system, the more you see what you are getting.

Fortunately for us, we purchased ours more or less at the end of a 3 year price freeze due to Covid. The current price is more than what we paid, but knowing now what we do, we would get another system if we had another truck.

We haven't regretted it one bit.
 

Joe917

Explorer
We had a similar system on our truck.
The external supply is extremely vulnerable to damage.
After ripping it of twice that was the end of the system.
 
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Peter_n_Margaret

Adventurer
The most recently built OKAs had CTIS as an option, but I am unaware of any actually fitted and sold. The air came in through the centres of the axles.
Cheers,
Peter
OKA196 motorhome
 

Ultimark

Active member
We had a similar system on our truck.
The external supply is extremely vulnerable to damage.
After ripping it of twice that was the end of the system.

I have no doubt that it is possible we may do the same thing, that said, with where we have been with super tight heavily overgrown sections and a wide for the track vehicle, so far we have managed to train line the truck on both sides high and low with the pipes, and coming out scot free.

An inboard system from these people is possible (anything is possible) but when we were getting our system fitted, parts were not available. As for the cost of an inbuilt, or inside piping situation over and above what we paid, I have no idea.
 

Ultimark

Active member
The most recently built OKAs had CTIS as an option, but I am unaware of any actually fitted and sold. The air came in through the centres of the axles.
Cheers,
Peter
OKA196 motorhome

Interesting about the hollow axles. I remember reading that a CTIS was available for the new OKA range, but that is all I knew.

Unicat in Germany, do their inbuilt CTIS on MAN trucks with special order hollow axles; saw a Unicat MAN in Iceland and spoke to the owner about it, among other things.

Mick.
 
I read a MAN truck brochure and gathered that CTIS is an option on many civilian models. At least several years ago.
MAN build or at least built militarized versions of their civilian lines for many militaries, where CTIS is pretty essential.
It’s possible this is old information from 2006 when I inquired with Thomas Ritter picking my U500 up, MAN has pretty well separated military and civilian lines since with the requirement for armored cabs now being ubiquitous. MAN HX is their current military line.
I have stated many times on this forum that the 3 features of my U500 camper that greatly augment mobility and self extraction ability (other than ground clearance) are:
Diff locks x 3
Very low gearing when needed (5.757 low range)
And CTIS.
Sometimes it’s the last one that makes the difference, takes maybe 3 minutes to properly deflate. Once unstuck, maybe 5-10 minutes to completely re-inflate while driving slowly.
 
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Ultimark

Active member
Charlie, you make an interesting point about deflating and inflating times. Not having any prior exposure to a CTIS it took a while to understand that our CTIS takes its time by doing both exercises in spurts. It will deflate the axles for a bit, check the pressure, then further deflate. As it almost gets to the desired pressure, it takes shorter pressure release checks. Now I'm not sure if is the software design doing this, or a mechanical one, but it certainly seems to slow down as it nears the desired pressure.

I'm also not sure if some of the frequent stops when inflating are caused by the ARB compressor playing catch-up, but I don't think so. During inflating, the ARB compressor shuts off while the CTI module is checking, then when the module bips again, which signals either air going in or out, the compressor kicks in again shortly after. It does this to both axles independently.

Is your Unimog CTIS individual wheel, or front rear axle controlled?

Our deflation times from road pressure to get us out of mud/sand pressure, are in the order of around 3 minutes as well, and interestingly, our inflation times from our bottom pressure to road pressure are around 8-9 minutes too, as we drive slowly with incremental speed increases in line with the increasing tyre pressures which can be seen live.

We don't have differential locks, just the standard Isuzu clutch pack LSD in the rear and an aftermarket Torsen torque bias differential in the front.

The Isuzu doesn't have great ground clearance, a big low rear differential sees to that, but reasonably low gearing, with, if I'm reading things correctly, a ratio of 5.571. Combined with the CTIS, it is now a pretty handy vehicle and can certainly climb or navigate difficult terrain in relative comfort.

Mick.
 
On modern Unimog factory CTIS installations, one can deflate or inflate one axle at a time, or both. But when one reaches limits predetermined by the yellow coding plug (I have 3 different ones), it will stop. So for inflation I do 1 axle at a time.
Without having to manually deflate, but using my lowest psi coding pluf, I can go down to 14 psi front and 23 rear. For highway I start at 63/95 in the am.
There’s a separate CTIS computer module. Naturally I have a spare.
I have Hutchinson 2 piece wheels with beadlocks.
Can someone please tell me what is the function of the “CTIS piece” in the picture to. Follow? Is it isolating air system unless pressure change is detected?
The little thing in the indent in the upper piece of the wheel?

second picture
 
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