Originally Posted by
DnvrFox
If 120 or 110 psi is good for a 700x25 or 23, why isn't it good for a 700x38? Especially when research (by physicists?) show that larger tires with more pressure have less rolling resistance, generally.
Because at the same pressure, the 38mm tire will be putting an outward pressure on the rim that is ~69% greater than the pressure imposed by the 23mm tire.
Source:
Understanding the Influence of Pressure and Radial Loads on Stress and Displacement Response of a Rotating Body: The Automobile Wheel
Download the PDF, look at page 3, section 2.2, formula 5.
Reference Figure 4 to see what the variables mean.