[sr_1445]

So we all know that Atmospheric Pressure at sea level is 14.7 PSI. I do know that we fill our car's tyres in relation to atmospheric pressure.
So my question is :
When I fill my car's tyres at 33PSI , is it 14.7 PSI +18.3 PSI(Atmospheric + Actual(?) Tyre Pressure) or is it 33PSI above atmospheric pressure?

Thanks.

[aah78]

Your pressure gauge is calibrated to read 0 psi at sea level / 14.7psi atmospheric pressure.

So the absolute pressure in your tyres will be 33psi + 14.7psi.

(Ignoring the effects of temperature here).

[dhanushs]

Originally Posted by sr_1445

So we all know that Atmospheric Pressure at sea level is 14.7 PSI. I do know that we fill our car's tyres in relation to atmospheric pressure.
So my question is :
When I fill my car's tyres at 33PSI , is it 14.7 PSI +18.3 PSI(Atmospheric + Actual(?) Tyre Pressure) or is it 33PSI above atmospheric pressure?

The drop in atmospheric pressure is also one of the reasons that the pressure in your tyres increase as you climb to higher altitudes. Basically, the number of molecules of air remain the same, but the effective pressure and its effects on driving change as you climb up and air gets thinner.