… Tire Inflation — Fostering Adventure

Tire Inflation Systems

Central tire inflation VERSUS Stationary Tire inflation

Tire pressures can make all the difference in how a vehicle performs on different terrains.

The ability to inflate and deflate tires on an adventure/overland vehicle is very important. Used for more than just re-inflating a flat tire after a puncture repair, an inflation system can increase or decrease tire pressures, allowing vehicle operators the option to customize tire parameters to best suit the surface they are traveling on. In other words, hard tires on hard smooth roads, and soft tires for soft or bumpy dirt tracks.

Spending an hour airing up in the morning before heading back onto pavement in Labrador, Canada. Notice the mosquito head net to prevent me from being drained of blood. Best ten bucks I’ve ever spent!

Although a simple stand alone air compressor and single air hose can accomplish the tasks outlined above, it can be a slow process. Especially on a large truck like ours whose tires are 48 inches in diameter and 15 inches wide. With a typical highway pressure of 110psi, multiplied by six tires, that’s a heck of a lot of air. To lower our tire pressures from 110psi to the desired offroad pressure of 50 psi, done one at a time using the standard Schrader tire valves, takes over an hour. Wasting an hour doing this is one thing, but doing it in a place like northern Labrador while being swarmed by hummingbird sized mosquitoes trying to drain you of every ounce of blood is something completely different. It’s at those times when one realizes that the relatively high cost of a multi-wheel tire inflation system seems insignificant since it can reduce that excruciating 60 minutes to a mere 5 minutes. And you can sit inside drinking coffee while it does it.

CEntral tire inflation systems

Hub based tire inflation system on a military truck rear axles. The air hoses come out of the centre of the wheel and into the conventional air inlet on the edge of the rim.

One of the things that is high on the list of desirables for expedition truck owners is a central tire inflation system (CTIS). This compressed air delivery system is built into the axles of the truck chassis when it’s manufactured, and supplies air through the wheel hubs to the tires. It allows the driver to inflate or deflate all the tires from the comfort of the driver’s seat, even while moving down the road.

But there’s a few issues with CTIS. One is that it is hard to come by on many trucks. CTIS is most often seen on military vehicles which are only available for the public to purchase as an older military surplus vehicle. On most non-military trucks it’s not available at all, and on those that it is, it’s expensive. Another issue with the CTIS is that it can be prone to leaks. The system is complex, with rotating parts and corresponding seals that must withstand air pressures of up to 130 p.s.i. (9 bar). Failure of any of these seals can result in deflated tires and a truck compressor that’s forced to work overtime. Worse than that is the cost of repairing the failure. Most often it happens in the hubs, and this means they have to be dismantled to replace the seals.

There is a “poor mans” aftermarket CTIS solution which can be installed on virtually any vehicle. It consists of air hose hoops that stretch from the truck body, over the outside of each tire and attaches to a coupling mounted on the outside centre of the wheel. It provides the same convenience as the axle CTIS system, is lower cost, but is very vulnerable to damage from anything brushing by the side of the wheels. These systems are most often seen on older transport trucks operating in under developed countries where treacherous roads are considered the norm.

stationary tire inflation system

Fortunately there is an alternative when CTIS is not an option. This is where the stationary tire inflation system (STIS) comes in. Although not quite as convenient as a CTIS, it’s almost as fast and certainly a huge improvement over having to tackle each tire, one at a time, using the conventional Schrader valve.

The main difference with the STIS is that you manually connect each tire valve to the system using a purpose installed air hose that’s located at each wheel. Each coil hose has a proprietary high volume, quick release air connection on it that attaches to the proprietary tire valve we installed on each wheel. In our case, once all six wheels are connected to the system we just dial the desired pressure, up or down, on the control box and all the tires air down or up simultaneously. Instead of taking well over an hour to do it the old fashioned way, it now only takes about five minutes.

A big advantage of the STIS is it’s relatively easy aftermarket installation. We bought our system from TI.Systems in Germany (https://ti.systems/stis/), and they supplied us with a complete turnkey solution with everything needed (except the tools) to complete the installation ourselves. The tools needed are few… a couple of wrenches, power hand drill and a few drill bits needed to provide the mounting holes for the included brackets and hose docks.

Our post-build Installation

The rear wheels facia triangle are where we wanted the rear air hoses to reside.

Although the installation of the system equipment is normally quite simple, ours was a bit more complex because of where we wanted to position the hose bays. The front bays were simple, but the rear ones we wanted to mount inside a storage box housed between the two rear tires on each side. To do this we either had to manufacture the boxes, or repurpose the existing triangular facia covers that existed already in those locations. Since making new boxes would impact the wheel flares and mounting hardware, we elected to repurpose the existing facias. This was a major pain because of the incredibly poor job the body builder did in fabricating these parts. Nothing was straight, square or properly mounted to the underside of the cabin. So along with making the enclosures, we had to repair those facia triangles so they mounted correctly.

The other small challenge was where we could put the control panel. It needed to be close to the truck’s main air supply, but also where it would be protected. On our truck, this ended up being on the opposite side of the truck from the trunk line for the rear brakes, nestled underneath the cabin right beside the entry door and stairs.

Step 1: CreatIng the mount for the control panel

The limited space on our truck exterior meant that we couldn’t use the control panel mounting bracket supplied by TI.Systems. So we had to design and manufacture our own.

The control panel comes with an air outlet for a single air hose for operating air tools or inflating tires and other things, and also comes with four 12mm hose connections for attaching the supply lines to each of the six coil hose bays. We plumbed up the distribution manifold right on the control panel mounting bracket that we made. This made attaching each of the supply runs to the control panel much easier.

The control box came with a quick release hose coupling. But we had to change it to fit our air hoses.

We had to rotate the gauge because we mounted the box on its side.

The sanded aluminum brackets were primed with an etching primer.

After priming, the brackets were coated with rocker panel stone guard paint.

Washers had to be added to provide clearance. They were held in place by the rock guard coating.

We test fitted the basic bracket to the truck to ensure it fits right.

Once coated, the control box was attached and the hose layout began.

The factory air coupling was at the back, so to reach it it had to be relocated around to the front.

We bought a stainless steel quick release coupling that fits our hoses and installed it with a cap.

Pre-installing the 12mm tubing with push connectors makes hose run connection easier on the truck.

We had to add a support bracket to the box plumbing to keep it from twisting when attaching a hose on the front connection.

A stainless steel pipe strap holds the valve securely to the bracket.

We also added heat shrink tubing to the joint on the left to ensure it was sealed.

Step 2: Fabricating the rear hose lockers

Attempting to build a waterproof box using an existing non-waterproof part.

A more tedious job than making the control box mounting bracket, the rear hose lockers had to be fabricated from light gauge aluminum and married up to the existing wheel well facia triangles. It was a challenging task as the triangles were poorly made with uneven angles and lots of distortion due to amateurish welding done by someone working for the bodybuilder.

For the hose tubes to fit in and be useable, the door on the front of the triangles needed to be as big as possible.

We were able to fit a useable door in between the fender flare rubber. Corrosion splotches show the builder used a cheap, non-corrosion proof alloy.

We had just enough stainless steel piano hinge left over from another project to do this job.

The oversized hinge centre allowed it to fold back with two layers of metal in it.

One challenge is to be able to seal the enclosure despite the gaps through the hinge itself.

The pan enclosure was bent up from .080” thick 5052 aluminum. A proper marine grade aluminum alloy that won’t corrode from road salt.

The pan was made just deep enough so the back of the hose tubes would press against the rear wall.

The two tubes had to be mounted slightly different because they had to be offset to accommodate the subframe support beam that was off centre to the centre between the rear axles.

A seal will have to be constructed for the flat door to press against.

Although the hose tubes have covers to protect the hoses, we wanted them inside a box because of the abusive environment right above the rear wheels.

When constructing the enclosure pan it needed to interface with the facia triangles, the two-level stepped underside edge of the cabin box, and the hose containment tubes. Basically, it was a nip and tuck operation where each side was done individually because of the differences from one side to the other. One would expect them to be the same, but in our case that would be wishful thinking.

Two door stops had to be made for the flip up doors to seat against when closed.

The door stops would be fronted with a layer of rubber to act as a gasket.

The box dimensions we such that the hose tube caps could be left on the tubes and held in place when the door is closed.

The two bent up pans were made to slip into the inside of the facia panel returns where they will be held in place with screws.

Once the pan was screwed in place, the rear of the enclose could be laid in place and the shape traced to fit.

For simplicity, the rear closure won’t have a return flange to screw tot he cabin underside. It will just be held with caulking.

Once cut and tacked in place, the rear closure was fully TIG welded in place.

The continuous weld imparts a lot of rigidity to the enclosure.

When the weld joint is well fitted, the two sides of the joint can be flowed together without any filler rod for a very fine finish.

A tab was extended to the side bolting flange to add strength to the corner joint so the weld can’t split open.

A cutout had to be made in the back to accommodate the subframe support brace.

A notch had to be made in the corner by the facia panel to accommodate the 1/4” thick edge angle on the corner of the cabin.

Before doing any finishing work we did a test fit on the truck.

The shape of the door allows it to open fully between the rubber fender flares.

The hose tube enclosures sit tight against the back wall so the air connections can protrude through the back.

This shows how the tubes had to be mounted in order to miss the subframe brace that penetrates into the box.

The door size is sufficient to allow the hoses to be extended out to the wheels.

When finished, the inside of the door will be covered with closed cell foam to aid in weather sealing. It will also help to hold the hose tube caps in place.

Since expedition trucks fall victim to vandalism and theft we had to fit door locks to the air hose lockers to protect them from unfriendly hands.

Fitting a lock to keep the door closed and secure was important. The “double-d” hole had to start with a round hole.

We had to get the locks first so the hole location could facilitate the length of the latch lever.

Since we didn’t have a “double-d” punch we had to use round and square files to sculp the shape needed to secure the lock barrel.

With the hole shape finished we could fit the barrel. When final installation is done the lock will have a snap-over weather shield.

The latch lever has an adjustable insert to ensure the door is pulled tightly shut.

The lock mechanism has a square end so the latch lever can be mounted to swing clockwise or counterclockwise depending on the need.

With the latch installed all that remains is to seal the enclosure and paint it.

This shows the rubber seal mounted to the door stop that surrounds the perimeter of the opening.

The final step in the completion of the rear hose lockers was to paint them. Rather than getting everything sandblasted and powder coated, most of which would get covered with gravel guard protection, we elected to simply sand the pieces to create a key in the surface for the paint, and then prime with an etching primer in preparation for the gravel guard and finished colour coat.

All of the components were hand sanded to prepare them for paint.

An automotive etching primer was applied to all the pieces using a rattle can.

Then all the individual components were coated with the thick gravel guard material for protection against flying rocks and debris flung up by the tires.

All sides and surfaces were coated for maximum corrosion protection.

Once the paint had cured for a few days the components were assembled so that additional coats of gravel guard could be sprayed on to help with enclosure sealing.

Since these enclosures were never going to be disassembled, we painted over all of the exposed fasteners as well/

Since the environment where these enclosures would reside was very abusive, many coats of gravel guard were applied over several days to increase the coating thickness and resiliency.

The underneath open areas of the facia triangles were also heavily coated so they would be sealed from moisture ingress.

Once the gravel guard coating was finished the masking tape that was protecting the areas that would remain smooth was removed, and all was colour coated.

Areas that didn’t need to be painted brown to match the truck colour were masked off and left black.

Since the spray paint was considered touch up paint, it was thin. So multiple coats were needed.

The doors were painted at the same time, and from the same can so as to ensure a perfect colour match.

All the exposed screw heads were also sanded, etch primed and painted brown so they wouldn’t stand out.

The back of the door seals were left the black colour so they would blend in with the interior colour. Details matter.

With all the painting of the components finished, final assembly could begin.

With all the painting finished and fully hard, the assembly process could begin. Through this process the other points of the enclosures where small leaks could occur are sealed up with foam rubber and caulking.

The spray paint turned out to be a perfect match in colour and sheen to the six year old powder coating on the truck.

The notches in the metal behind the hinge area is to provide clearance so the swinging hinge doesn’t scrap its paint off.

This shows the door seal which is held in place with facia screws as well as the latch securing point. All but two of the screws get covered with the fender flare rubber.

Along with bracing the door seal, the latch anchor point also provides strength to the top face that screws to the box underside.

The hose storage tubes were bolted in place and then all the penetrations caulked.

Once the caulking was fully cured several more coats of gravel guard was applied to encase the caulking.

The hose tubes sit nicely inside the enclosure with their caps on. The rear caps were sealed with caulk to the inside of the back wall.

The inside of the door and floor were covered with closed cell foam for weather sealing. The small squares are to hold the tube caps on tightly.

This shows the lock latch in place behind its anchor point.

We pre-installed the airlines on the enclosure box so it was easier to install on the underside of the cabin.

Step 3: STIS truck installation

The control box is located on the curbside of the truck just behind the fuel tank. It’s convenient, and on the safe side of the truck from the traffic.

Now that all the components are completed the final installation on the truck can be done. The first thing to install is the control box, as this is where all the air lines to the remote hoses begins, and from where all the airline lengths must be measured.

Next the air hose storage lockers and tubes need to be installed so the other end of the airline dimension was fixed. Then it was a simple task of cutting the airline to the appropriate lengths and running them along the frame.

Mounting the base bracket for the control box was first. It was lag screwed into the fiberglass structural bracing on the cabin underside. Caulking was used to seal each screw.

Next the control box with its attached backing plate was bolted to the base bracket.

The airline connections extend off the back of the backing plate ready for hookup.

The finished rear hose lockers were bolted into place using lag screws into the cabin underside.

Heavy beads of Sikaflex 291 caulking were applied to all edges and flanges that interface with the underside of the cabin.

The lag screws were not done up tight, but we’re left so there was a 1/16” (1mm) gap. This ensured that not all the caulking was squeezed out. Caulk will also act as a glue.

The front hose storage tubes were bolted to the step floor we previously installed.

This location is ideal for the front tire inflation hoses.

Now that the inflation hose storage units were installed we were able to determine the final route for the airlines along the frame, and consequently the final lengths of the airlines. Although the airline material is 12mm poly tubing with a 1.5mm wall thickness, and therefore very robust, we decided to wrap sections that would be exposed to abrasion or flying debris abuse with an industrial plastic spiral wrap material used for hydraulic and pneumatic hose protection. TI.Systems also provided a corrugated protection casing which we used in the wheel well areas.

Once the lengths were determined, the airlines were grouped together for front or back runs.

The best route along the truck frame meant the front lines and rear lines would be run along the same side of the truck. This allowed the spiral wrap solution.

The spiral wrap comes in various sizes, so we were able to use one that perfectly fit around two airlines.

The plastic airline is very stiff, so to create tights bends it is wise to heat it using a hot air gun. By holding the bend until it cools down, the bend maintains it shape.

With the tight bends made and wrapped with spiral protection, we pre-installed the push-to-connect fittings.

The open ends of the connectors were plugged with temporary tube ends so dirt couldn’t entry when fishing the lines through the frame.

Heavy zip ties and stainless hose clamps secure the airlines to the cabin subframe.

After the airlines were cut, bent and spiral wrapped, it was just a matter of feeding them along the frame rails. In the case of the front lines, the wrapped pair was actually fed inside the main truck frame rail, past the exhaust system and engine up to the very front. The rear lines were easier, fed just underneath the cabin box, behind the entry stairs and the generator. They were fastened to the underside of the cabin box with stainless steel hose hangers and stainless steel lag screws. When they reached the back they were fastened to the subframe with heavy duty zip ties and stainless steel hose hangers.

The front axle airlines are connected to the bottom of the control outputs and are held firm to the subframe with a clamp. That way there is no strain on the connection.

The front double airline travels over top of the truck frame to the inside open area. It’s attached to the cabin subframe so no stress is put on the connections.

The front double line hangs free from the subframe clamps to the truck frame point. This so it can move as the truck frame twists.

The front airlines split with the right side following the existing hoses up to the right hose storage tube.

When the airline connection is made and the release locks inserted, the joint is wrapped in a vulcanizing tape to protect it.

Despite the addition of the hose storage tube to the area, there is still ample room to stand on the floor for maintenance and window cleaning.

The left side front air line was routed under the radiator where many other lines travelled, and then up onto the bumper floor to the connection.

Like the right side, the connection was locked and sealed.

Each push-to-connect fitting has release collars which when pushed in allows the hose to be pulled out of the fitting. A locking clip is installed to prevent accidental release.

Once the locking clip is installed, the fitting is wrapped with a self vulcanizing rubber tape to protect the locking clip and offer redundant security.

The angle of the hose storage tube, like the right side, is oriented to point toward the wheel it will interface with.

This shows the main distribution point of the STIS.

The rear double airline is clamped to the underside of the cabin in two places until it reaches the rear wheel wells.

When the rear double airline reaches the wheel well area it is then attached to the cabin subframe with heavy duty zip ties.

The two rear airlines are zip tied to the subframe as they diverge to the two sides of the truck rear axles.

The rear right side hose was fed through the main body mount and back to the air connection.

Stainless steel hose hangers were fastened to the subframe so the hose moved with all the components as one.

On the back connections, more robust protection was used to protect the connector and locking clip once it was secured.

This shows the left rear connection before the locking ring is inserted in the silver fitting and the protection sleeve slid over and clamped.

The left rear airline snakes across the width of the frame from the right side where it splits off from the right airline.

The corrugated protection sleeve supplied from TI.Systems completely encases the plastic airline wherever it is exposed to flying wheel cast-off debris.

As the heart of the system, the control box is connected directly to the main rear brake line that comes directly from the trucks engine compressor.

Separated from the brake system by a ball valve, air is only supplied to the STIS control box when the inflation system is needed.

Air pressures from 0 to 10 bar (145psi) can be dialed up as needed. The air hose outlet below the box bypasses the control box and is always full line pressure.

The control box is protected from flying rocks by an aluminum shield.

One of the last things to do to finish off the installation is to install the weather caps on the locks.

The weather caps not only keep debris out of the key hole and lock mechanism, but also help to prevent water ingress to the storage locker.

Along with the lock weather caps, eyebrow drip covers were made from .040” aluminum.

These eyebrows prevent water from running down the outside wall, and onto the hose locker where it could seep into the door seal.

The aluminum eyebrows were well sanded and then primed with the automotive metal etching primer before the colour topcoat.

The final paint coating on the eyebrows was done with the Cardinal colour matched spray paint that Cardinal produces as touch up paint for the powder coating we used on the truck.

Step 4: The final process… tire vaLve replacement

8 wheels x 2 valves per unit wheel = 16 valves to install. Going to need a few cups of coffee for this one.

The last step in the process of installing the STIS on the truck was to install all of the special high flow tire valves in our Hutchison aluminum wheels. Since our Hutchison wheels are reversible, they have valve stems on each side of the rim. This means that we have to install sixteen valves, and to do the ones on the backside of the wheels, the wheels will have to be removed from the axles.

Our valve stems are not like those in conventional rims. Those valves are made with a rubber bulb at their base, and the valve is inserted from inside the rim and then pulled through from the outside until the bulb seats. Removal is as simple as using a knife to cut the base of the valve stem.

The 1/4”MPT Shrader tire valve on the back of our Hutchinson rims.

In our case, however, the Shrader valve stems in Hutchinson wheels are metal, and screwed into the aluminum wheel using a 1/4” male pipe thread. To change the valves we have to first deflate the tire completely to ensure that when the old valves are unscrewed, they don’t fire across the parking lot when the final turn of the thread takes place. Then it’s just a matter of cleaning the internal threads before screwing in the new valves with some thread locker/sealer.

The old Schrader valve compared to the new STIS valve.

The standard TI.Systems STIS valve stem with supplied protective cap.

This shows the valve stem with the quick connect air hose connector.

The valve stem and air connector are of high quality, made in Germany.

When the connection is made, it is solidly locked in place until the release collar on the connector is physically pulled back to break the connection.

TI.Systems also supplies an adapter so that the TI.Systems valve stem can be inflated with a standard Schrader style air chuck.

The adapting connector is a nice tiny package that can be easily stored anywhere.

All Complete And Ready For Use

Airing the tires back up from 0 psi, as we had to deflate the tires completely in order to swap out the old valves for the new ones.

With all the components installed, our system was ready for final testing. With the dozens of connections that were made from where the system was spliced into the main airline of the truck, to the terminus of each coiled air hose, there was a lot of potential for air leaks if we hadn’t properly sealed each threaded joint. Fortunately, we had no leaks. When we energized the STIS, and then closed the valve that isolates it from the truck system, the STIS held pressure overnight. So we were very happy about that. All we had to do to complete the job was to install the locks on the doors of the rear hose bays. We even found some weather proof caps to enclose the locks so they would not be damaged by the harsh outside environment of the rear wheel arches. A nice touch to finish off a rather time consuming addition to the truck.