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Old 15th January 2014, 13:44   #1
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Question The 'Actual' Tyre Pressure : Is Atmospheric Pressure Counted?

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.
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Old 15th January 2014, 23:04   #2
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Arrow re: The 'Actual' Tyre Pressure : Is Atmospheric Pressure Counted?

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).
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Old 16th January 2014, 11:05   #3
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Default re: The 'Actual' Tyre Pressure : Is Atmospheric Pressure Counted?

Quote:
Originally Posted by sr_1445 View Post
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.
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