the 3.75 allows you a different option in tires. I run 3.5 as I run the 120/70R17 front tire and like it just fine. I went for the same size for the second set of rims (over the 3.75 front).

I think the 3.75 front rim would need a 125/60 front tire. Might give you a more flatter profile then the 120/70 on the 3.5 rim.
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Charles Gallant