Now a tire mostly have about a gauge pressure of a 30 psi, and the gauge pressure is the pressure above atmospheric pressure, and the atmospheric pressure is about 14.7 psi, does that mean that the gauge pressure is actually 15.3 psi? because instruments measuring gauge pressure takes atmospheric pressure as a starting point (0)
[Physics] Gauge pressure and atmospheric pressure
pressure
Related Solutions
The shear and tension stress on the material would be the same, because only the difference matters for that. So for testing strength of the structure the cases are equivalent.
The material would still be under the total pressure though, so if the material itself can't withstand that pressure, it would degrade (it may change crystalline structure, compounds may undergo chemical reaction and such with corresponding change in modulus of strength; or it may just break on inhomogeneities and crumble). However solid material generally withstand significantly higher pressures.
And under water there is also higher difference between pressure on the top and bottom surface and corresponding difference in buoyancy.
You should be fine as long as you are consistent. If you use total pressure, as they do, then you also need to include the effects of the air pressure on top of the tire pushing down on it with 1 atmosphere of force!
As a thought experiment let's use some really fancy spherical-cow materials. Let's make a gigantic tire out of material that has negligible mass and put 100kN of force on it. If we pump the tires up to slightly above atmospheric pressure, say $P_{gague} = 0.00000001 kPa$. These are the flattest tires on the planet!
By your method, using just gauge pressures, you would see that these tires would flatten out like pancakes until their area was massive.
By using their method, converting to absolute pressures, $P_{total}=101.00000001 kPa$, so by $A=\frac{F}{P}$ you would get an area of 1 square meter or so. This would be an absolute minimum. No matter how flat your tires are, they would never take up more than a square meter to support 100kN. Something's wrong!
On the other hand, if you use all absolute pressures and you account for the fact that there's atmospheric pressure pushing down on the tires as well as the weight of the vehicle, then you would once again be able to show that the world's flattest tires are, indeed, flat.
Best Answer
No. The gauge pressure outside the tire is 0. The absolute pressure inside the tire is 44.7 psi in your scenario. See this related question for details: Gauge pressure vs. absolute pressure?