there isn't a set length requirement per se. it really depends more on the comfort of the string angle at full draw. i am currenlty shooting a 34" ata bow with no problems. the finger pinch doesn't bother me at all and i am shooting 3 fingers on the string. i know some guys who are shooting only two fingers on the string to keep string pinch to a minimum. i guess it all depends on how comfortable you feel the bow is at full draw. i will, however, be buying a bow near 40" ata for my next purchase, as i feel i shoot better with longer ata bows...do a search in the archives for posts by Arthur P. he has had some very informative posts on this very topic...