What tire pressure numbers to trust (deflator gauge or on-board tire pressure computer)?

I'm using a Jaco precision tire pressure deflator gauge, but the readings are consistently 5 PSI lower than the on-board tire pressure computer. Anyone have a good idea which one to trust or how to mediate between these readings?

This is the item I'm using: https://www.amazon.com/dp/B01ETWXEWA?_encoding=UTF8

I'm using BFG KO2s at 36 PSI.

 

The only thing I could recommend would be to try another gauge and see if it matches one or the other. I don't tend to trust digital gauges.

 

I use those cheap tire gauges from Walmart. I think it’s $4 for a metal gauge instead of the plastic gauges.

 

It's a 200psi gauge with an accuracy rating of + or - 1% per 100 psi. For true accuracy you need to compare its reading to at least one or two other gauges. Preferably gauges that top out below 100 psi but within your intended range of inflation.

 

Probably an exercise in splitting hairs at this point. In all my years of driving, I’ve yet to see any direct correlations between reasonable tire inflation pressures and tire wear, mpg or handling. If you go with the computer’s readings, at least your vehicle will have that info on board in the event of an accident. But personally, I’ve never sweated that detail.

 

I've used an ARB deflator for years now and have always had accurate readings compared to a higher end setup I'd compare it to.

 

The gauge you list on Amazon says " it's performance tested and highly accurate", do you feel the same about the 'onboard' TPMS? Exactly.. We use a gauge, and we use the same gauge all the time, that somewhat eliminates variations instead of using different gauges periodically. We also notice a difference in the TPMS and our gauge, give or take a couple of pounds.

 

I use a Viair tire deflator. Works good. Not super fast but not that slow either.