They don't flap around as much as you'd think. The one I have --I think it's made by Vaude--has a cinch strap around the waist, and finger straps that keep it planted firmly on the hoods as you ride. In heavy rain, you get a puddle between your arms, but that's easy to shake off. It works surprisingly well. Where it does not excell is really cold and nasty rain, below, say, 38 degrees. The cape retains no warmth, and you can feel every gust. But mid-40s and up, it works well.