I made one of these things for the race up Mt. Washington in the mid 70's. I figured I needed all the help I could get, and a low, low gear to get me up that hill. I cut the web from an outer TA and bolted a 30-something tooth ring to it. Slapped it on my Geofrey Butler and crawled up. OK, so I lost a little time on the flat part before the turn into the trees.....
Mark Hoffman
New Britain, CT