I've got an ongoing research project. Perhaps it's destined to be a lifetime research project. Let me explain.
As the days get hotter, and the pavement gets correspondingly hotter, how does it affect rolling resistance?
1) On the one hand, we've all seen water droplets "sizzle" across a hot skillet. Do bicycle tires "sizzle" on the pavement surface in similar fashion? Which would decrease rolling resistance, one would think.
2) Or, on the other hand, we've all seen how a cube of butter melts on a hot skillet, increasing the "contact patch" and becoming generally less wieldy. (Surely melted butter has more "resistance" than a solid stick of butter!)
So far, my research has been based solely on personal observation. And even after many years, the results are "inconclusive." I will continue to observe. Input from other "guinea pigs" would be welcomed!
(I'll be disappointed if I've spent so much time and effort, and somebody tells me "there's an app for that," available on your smart phone!)