First Published on October 12 2018
Dual Tyre Pressure Equalisation and TPMS Setup
Clarence our VW LT Campervan Conversion is the 4.6tonne model, and as such is fitted with Dual Rear Wheels (or a ‘Dually’ in general terms).
A Dual Wheel System refers to a setup where there are two wheels either side, using the same Axle for all 4 wheels. A system with 4 rear wheels using a pair of Axles is usually referred to as a Tag Axle system and is common on larger Motorhomes.
The term ‘Twin Wheels’ is meant to mean a Dual Wheel configuration but often people use it instead of a configuration with a Tag Axle.
This ‘Dually’ type of setup can be awkward to keep an eye on pressures, so I bought a 6-wheel TPMS (Tyre Pressure Monitoring System) for it. However, I had problems with it as the extra weight of the sensors on the Valve extenders (needed to access the tyre valves) tended to cause the elbow extender to loosen and so loose pressure. The extender actually had loosened a couple of times even without the sensors so was a hassle.
I searched around the internet for options and came across the Crossfire system and really liked the sound of the features.
This is the manufacturers web page on the product – Crossfire – Dual Dynamics – and a video of how the system works.
You need to choose a kit that matches the Pressure you want to run at – they are not adjustable. When I first looked at these I was not sure what pressure I would be running the rear tyres at as didn’t know my final running weight. Once I had near enough completed the conversion, loaded up with the most I planed to carry (which is quite a bit in the garage sometimes), took to the weighbridge and from that weight reading and further research, decided 65PSI would be the pressure of choice for my rig.
These kits don’t seem to have come over to the UK or Europe so an US reseller is pretty well the only option for purchase. Looked for the best price for a 65PSI Crossfire kit and as luck would have it found a nearly-new pair of 65PSI units on Ebay.com (US Site). The units with postage and import duties came to around £60 which is very good.
Installing the Crossfire System
Installation was a bit trickier then the instructions and youtube videos would have you believe though (at least on my vehicle). In order to properly secure the hose on the inner wheel I had the remove the outer wheel to allow room for the 13mm spanner to tighten the hose nut. The sequence of fitting like this means you lose pressure while the Crossfire is partly disassembled (but not a big problem and actually means you get to check its operation as part of the install)
Overall, including jacking up the van each side, removing a pair of wheels, installing the kit and refitting wheels, retorquing, dropping jack and packing away took maybe 60 minutes.
Once Installed this is what it looks like on a LT/Sprinter Dual Wheel
When at the pre-set Pressure, the display is Yellow and there are two black marks that line up with the marks on the surround
This shows the Yellow section coming into view as I am inflating the tyres up to pressure
When the pressure is 10PSI below the pre-set, the display is black. This shows mostly black as I am at around 55PSI
If the pressure is 10PSI OVER the preset the display shows red. This is quite possible to happen due to the way tyres warm up and it is more of a informational display rather then a problem one. Very much as expected and described by the maker – over pressure due to the heat induced when driving. Being half yellow, half red I would estimate 70 PSI (as 10 PSI down changes from full yellow to full black and I’m guessing the change is linier).
What I really like about this system is not just it tells you at a glance the pressure is at the setting you want when you do your walkround before driving off, but it keeps the tyre pressures matched between inner and outer tyres, plus it gives you just one fill valve for both tyres which is dead handy I think.
(To pre-answer one common question on this system, the unit is monitoring both tyres and if one tyre suffers rapid deflation, the valve shuts off. For a slow leak, the valves shut off when the pressure drops 10PSI below the preset (so 55PSI for me))
Adding TPMS
The Crossfire system gives you an indication of the rear pressures but I like having a TPMS setup installed to give live info on Front and Rear tyres. There was a bit of a delay with the TPMS as when I installed it most of the sensors didn’t seem to work. When I checked the batteries, all but one was under 3V (uses 3V batteries). A little surprising as the kit was only fitted for a few months, but hey-ho.
Bought a pack of batteries from Amazon, fitted them and reinstalled the sensors
They look nice and neat on the Crossfire unit as well.
Now as I mentioned, the TPMS system I got was a 6-wheel setup – designed for either Vehicle + Trailer or a 6-wheel vehicle (the display actually represents a Dually). I bought this before I was aware of the Crossfire system and wanted to monitor all the wheels.
With the Crossfire system installed, I have two extra sensors now seeing as the Crossfire combines each pair of wheels and presents a single valve (as shown above). So what to do with the spare sensors? I was going to fit them to my trailer, but I don’t really use the trailer much, plus it doesn’t seem possible to set the second set of rear sensors differently to the first set, so the pressures would not be right.
I noticed that the TPMS kit has an option for a Spare Wheel sensor. So this is what I did! Recoded one of the spare sensors to become the Spare Wheel sensor, and left the last sensor without a battery (so it isn’t been picked up and showing as low pressure) to keep as a general spare.
So 4 main wheels show in the display above.
The display alternates between the primary and secondary sensors. The one pictured here is showing the spare
I need to recode the last sensor to remove it from the default 2nd dually wheel so that wheel doesn’t show anymore at all, but only takes a few minutes to do.
It is quite a neat TPMS system. I do like the fact it uses a little solar panel to keep it charged so not tied to being wired up for power. And in conjuction with the Crossfire system I have a very good monitoring system to keep an eye on all the tyres on what is a fairly heavy vehicle.
If you are interested in a TPMS system, or just would like to know a bit more about them, drop a reply comment to this thread (and the same if you have questions on the Crossfire system). I have been using and fitting Aftermarket TPMS systems for nearly 20 years and think they are a great safety addition to any vehicle!