I ride a Trek 420 (commuting) here at school and I have 38's, I believe. Perfect fit. I was doubtful they would fit but I just went for it.
This is probably more believable with pictures so I may add some later, no rub except a tiny bit on a reflector bracket on the brake bridge, which I plan on bending a little bit to get out of the way.
All my other bikes get the skinny tires though.
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