As I recall previous discussions on this topic, the concern for spreading is
the weakness imparted on the seatstays at the brake bridge. Purists recommend
you have a framebuilder actually redo the brake bridge for the wider spread.
I believe it was Mike Kone who suggested "sighting" down the seatstays of a
spread frame and looking at the bend that occurs at the bridge. I also recall
Larry Black pointing out that we are talking about the width of a couple of
spokes on each side too, so that made me think that the stress can't be too bad.
I don't have a lot of experience at this. I've run thousands of miles with "temporary" spreading from 120 to 126 and 126 to 130 but I suspect that is probably a no-no for a nice frame. Lou Deeter, Orlando FL