There's lots of good advice (98.6% of it from me) in this forum if you search.
It depends on wheel size, tyre section, experience, ability, terrain, style...
But 125 is a reasonablle all round size for a competent rider on most wheel sizes for anythign except very high speed or extreme muni.
-- Mikefule
"We begin in the madness of carnal desire and the transport of voluptuousness; we end in the dissolution of all our parts and the musty stench of corpses." Arthur Schopenhauer. Philosopher and pessimist. ------------------------------------------------------------------------ Mikefule's Profile: http://www.unicyclist.com/profile/879 View this thread: http://www.unicyclist.com/thread/52816