Right when I were a lad.If you were over six foot like I was,you bought a 25" frame. Then we went all fancy,and it was a 64cm job.Then things changed again,we got sloping top tubes.Now just this week I have been looking at cycles for a more slower but longer type of riding ie Audax and it seems 58cm is now big enough for a bloke 6' 4" tall. Can anyone explain.