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EFI Tuning Fundamentals

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Might be a stupid question, but can someone explain in a little more detail how absolute pressure gague reading 40.7 psi and when connected to a tyre with 35psi of air in in would measure 49.7psi in absolute pressure.

I cannot get my head around it.

The world is in a constant pressure (barometric pressure), which is 14.7 psi at sea level on a good day, on a gauge it will read 0psi.

absolute pressure = gauge + atmosphere

So for your example, the gauge pressure of the tyre is 35psi but for the total pressure (absolute pressure) it is 35psi+14.7psi=49.7psi if you were at sea level, if you are at a higher altitude or in a weather system with a low pressure then your atmospheric pressure won't be 14.7 any more, it could be 9.7psi. 35+9.7=40.7

it's either that or the gauge is faulty.

EDIT: it's also worth noting that pressure gauges for tyres are reading the pressure differential, the difference in pressure from the inside of the tyre to the atmosphere around it

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