I've had hair between chin- and shoulder-length for most of my life. I hate having it tied back and only ever do so when I'm in the shower or the bath and don't want to get it wet. Unless it's really windy, I don't have a problem with it under my helmet - I just tilt my head back and make sure all my hair is out of the way before I put the helmet on and it seems to stay there. I guess it depends what you prefer ordinarily; if loose hair drives you mad anyway, you'd probably hate it that way under the helmet too.