I’m no mathematician so I’m unaware of how to calculate the speed, but in ISF’s defense the article I found reports the same speed he provided.
https://www.google.com/amp/s/www.mot...-07/16401/amp/
Edit: sorry I missed the part about basing the average speed on the precise measurement of the track. I’m guessing that article is offering the speed for if the track were exactly one mile, though I guess a track’s size can depend on the line you’re running which is an entirely different conversation lol.