Wheelbase, baby! either longer chainstays, toptube length, more fork rake, headtube angle or any combination thereof... My old '75 Fuji S-10S has a longer wheelbase than most '23"-frame' bikes of the same vintage... makes for a more relaxed (less 'twitchy') ride.
__________________
'75 Fuji S-10S bought new, 52k+ miles and still going!
'84 Univega Gran Tourismo
'84 Univega Viva Sport
'86 Miyata 710
'90 Schwinn Woodlands
Unknown brand MTB of questionable lineage aka 'Mutt Trail Bike'
Plus or minus a few others from time-to-time