Interesting study, Mark. I've always wondered how different mile measured splits might end up being when, for instance, I measure a marathon like Baltimore, which requires many hours, where temperatures rise and fall over the course of the measurement, causing mile splits to increase midday and then decrease a little towards evening - as they would be revealed to be if measured via steel tape. I have yet to hear any complaints.
Your research project would seem to me to imply that the differences in constant attributable to the tire types you tested aren't large enough to cause concern. Do you agree?
I wonder, like you, if a solid tire would produce radically different results. I also wonder if the coming "Smart Tire" or one of the other airless tires in development would produce significantly different results. What are your thoughts?