For lots of people, yes. The bike in the photo that Neal posted is running 38mm Pari-Motos (if I remember correctly). But they are touted as being exceptionally supple tires as well. I would say that for conversion, the candidate frame should fit at least 38mm tires with room to spare. On my converted frame, I can fit 42mm Hetres with about 3mm of clearance between the chainstays.