“Not correct. The pressure is stretching the tire and the cords it’s made of. Ever tune a guitar? You’re stretching wires as you do it.”
Steel probably does not stretch enough to matter at the stresses of a normal tire pressure. When you tune a guitar, you are probably distorting the wood more than you are stretching the steel.
It’s the steel e string on my fiddle that needs the most retuning, the non steel g, d, and a stings seem to hold their tune once they have been on the instrument a few weeks and the new string stretch has stabilized. That’s because it’s the steel string that doesn’t strech when the wood in the instrument changes dimensions due to humidity or temperature changes. This lack of stretch causes changes in string tension when the wood changes dimensions.
Also, a lot of guitars have been damaged by people who assume that the sharpest string is the one in tune and tune the rest of the stings to it. After repeated retunings, the pitch can be walked up to string breaking or bridge pulling off tension. Expanding wood can make a guitar go sharp as well as contracting wood can make a guitar go flat. It’s always best to tune to a reference pitch.
I didn’t say steel doesn’t stretch at all, if that was true, it couldn’t be used for springs. I just don’t thing your tape measure can measure the difference in a steel radial’s tire circumference between an underinflated and a overinflated tire.