Interesting article from the NYTimes looking at the geography of college football fanbases.
Michigan ends up with the second largest fanbase, behind OSU. Although it is tough to see Michigan behind OSU in anything, I think having an entire state essentially to themselves makes the difference. I would (like to think) that outside of their home states M still has an advantage over OSU. But splitting the state with MSU and Michigan having a smaller population than Ohio make the difference.
Breaking out some of the numbers:
Total number of fans for Michigan schools:
gets us to 4.24M fans Michigan gets ~68% of those fans.
Total number of fans for Ohio Schools
gets only 4.25M fans and OSU gets a 75%
I think that somewhat hold my theory. Michigan loses a much larger share of fans - both locally and to a lesser extent nationally to MSU. While the Buckeyes only lose tiny amount to their state schools.
I would be interested in seeing how the markets within Michigan broke down. I bet SW Michigan is a 3 way fight - with Michigan maybe even third behind Notre Dame and MSU. Michigan likely still dominates in Detroit. The rural areas I would guess are slightly Michigan, but that is based more on historically better program more than anything else.
I would be very interested to see this tracked over time. I would have thought ND would have come out first. They likely would have in the 1940-60s. Before the NFL took over NYC in the late 1950s, I would think all the numbers would have been a much higher percentage - but especially in the east.