Air up or air down all 4 tires at the same time? This was in the most recent issue of Land Rover Owner:
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At $300 US, it's seems a bit pricey to me. Coincidentally, I've been experimenting with the same idea, but using much less expensive parts. Mine is just a proof-of-concept prototype, it's not finished yet, but it uses 4 clip-on Schrader chucks, a 4-way valve assembly, a Schrader valve for connecting a compressor (or letting air out) and a pressure gauge.
It works as expected, which means I can air up or air down all 4 tires at the same time, monitoring the pressure on the gauge. The cheap hose I first used is prone to kinking, so I talked to a hose supplier I've worked with in the past to find some better hose and he sent me a sample - that's the black hose in the photo below. The new hose is perfect. A smaller digital pressure gauge would be better for this application, so I'll source that and get enough of the back hose to replace the kink-prone clear stuff.
The initial testing suggests this could be very useful not only on the trail but also useful to synchronize all 4 tires to the same pressure so the JKU's TPMS system will show all 4 tires being the same. And a lot less expensive than the UK product. I believe there's at least one similar product in the US, but I think it is also kind of pricey.
My project has the interest of a compressor company and I'm meeting with them at SEMA this week to discuss this and a few other ideas I've got for them.