I am concluding from our discussion and from Pete's article that narrow, high pressure bike tires tend to perform better than the hybrid bike tires I now use. My using nitrogen in them may have attenuated some of the expected expansion and contraction due to road surface and ambient temperature. I am thinking that switching to a narrow, 100+ PSI (pneumatic) tire filled with 95+% N2 may give me the best bang for my measuring buck.
"There are several compelling reasons to use pure nitrogen in tires. First is that nitrogen is less likely to migrate through tire rubber than is oxygen, which means that your tire pressures will remain more stable over the long term. Racers figured out pretty quickly that tires filled with nitrogen rather than air also exhibit less pressure change with temperature swings. That means more consistent inflation pressures during a race as the tires heat up." - Popular Mechanics, referring to car tires (only). Yet, I assume that stable pressure advantage also applies to bike tires.
"By reducing the percentage of oxygen, water vapor and other gases in your (bicycle) tires from 22% to 7% or lower, your tires will maintain proper pressure longer than if you use “plain old air.” For example, with 95% nitrogen in your tires, they retain optimal pressure three to four times longer." - A biker blog
I have never tried solid bike tires. I worry that the ride could be more tiring when measuring a marathon or even a marathon. What advice can you offer me about this?