How much air pressure for road bike tires?

I've seen a few posts here and there talking about the pressure run on road bike tires. Some tires are rated for higher pressure than others, but predominantly road bike tires are rated at 120 PSI. Personally, I only inflate my tires to 100 PSI. However, I recall a conversation I had with someone who was riding in a century race shortly after I had just bought my rode bike and they said that they had a blow out on a smooth road. The ambient temperature was near 100 degrees and the road surface was asphalt and blacktop. I'm curious by nature, so I decided to get all scientific about this. Granted, he could have had a defect in his tube, rim, or tire, but I'm going to assume that all was perfectly normal with his gear. Instead, I'm going to focus on the amount of pressure he had in his tire. It's a scientific fact that as the temperature of the gas rises and the volume stays constant, the pressure increases. How much is what I wanted to know. So, I calculated a scenario with one assumption; the internal temperature of the air in the tube. I believe during a hot summer's day here in California, the temperature of the asphalt on a road can be well over 120 degrees Fahrenheit. So I estimate that the internal temp of the road bike tire to be around 105 degrees Fahrenheit in my calculations.



I assume that the tire is inflated in the home at a temperature of 75 degrees Fahrenheit to a pressure of 115 PSI. Like I said, I personally do not exceed 100 to 105 PSI. But, if a person inflated their tire to 115 PSI and the internal temperature rose to 105 degrees Fahrenheit, the pressure would increase to over 121 PSI. This exceeds the rated pressure for the tire. If the pressure was originally at 120 PSI at 75 degrees Fahrenheit the pressure would rise to 127 PSI at 105 degrees Fahrenheit. This could contribute to the blow out scenario. If the temperature exceeds 105 degrees Fahrenheit, which it probably could, the pressure would be even higher.

So, be mindful of the tire pressure you use and the temp outside / potential temp of the asphalt.