I remembered an article from a popular science and looked up. It is on a bike called the ride and it's made by Ellsworth bikes. I don't know how to give any links but it has an infinite gear ratio. The rear hub has ball bearings that roll at varying angles between two discs to change the gear ratio. It is a three grand bike but an awesome idea that was thought of by leonardo da Vinci. Check into it and think what it could do for mb's.