One of my theories is that the energy required for a particular day’s ride correlates with the number of crank revolutions. A distance ride on a 36" with 150mm cranks is easier than the same ride on a 29er with 110 mm cranks, not because you can go faster on the 36 (which you really can’t), but because you have fewer pedal revs. For the same reason, a geared 29 with 150mm cranks will be less tiring than an ungeared 36er.
But then I’ll be the annoying person to bring in some real-world information:
Tire diameter is usually pretty far off from the exact number of inches printed on the side. It’s actually pretty amazing how far off some of them are.
Then there’s the annoying fact that we mostly can’t ride in a straight line. Do we count this in our calculations? My short answer would be no; that the correct # of revolutions to cover a mile has covered a mile. It might be a squiggly mile, but a mile it was.
Lastly I’ll add that I am happy to have a geared hub, to cut down on those big numbers of revs!