I have a Zzipper fairing that I bought in the 80's for use during cold Canadian winters. It worked tremendously well to protect your privates and hands during -30° weather. I would not go out in temps like that without a fairing. I also used it on a tandem and on descents it did indeed help. I had founded a tandem club and I rode with two main stokers and when coasting downhill with the Zzipper, we would regularly pass other tandems that would be just as fast as us on any other day without the fairing. The higher the speed the bigger the difference.