I am experimenting with running an old '83 Trek "road racing" bike with 12 speeds as a single speed. Shortened the chain, and have it running at 42 x 17, or 67 gear inches. This is a bike that I'm mostly using around my inner-city neighborhood, with stop signs or traffic lights every two hundred yards or so. Stop and go...stop and go.

So far, 67 gear inches seems to work well for "round the neighborhood" riding. It is easy to stop at a red light, and then spin back up to cruising speed. The combination of just 67 gear inches and half century old legs means my cruising speed looks rather slow to the younger guys who go whizzing past me on the road.

But, easy spinning in an easy gear has been helping my aging knees. When I wake up in the morning, my knees are a bit stiff and sore. After an hour or so of riding in an "easy" gear at 80 RPM's or 90 RPM's, my knees and legs feel good - the soreness and stiffness is gone. I finish a ride feeling about twenty years younger than when I got out of bed.