I want to build a single-speed-ish bike out of my '82 peugeot road bike conversion that will have a single freewheel gear out back but two chainrings that will yeild roughly 50 and 70 gear inches, respectively. This would allow me to move pretty fast on the road but still climb some pretty serious offroad stuff. I would shift simply by moving the chain with my finger when the bike is stopped so I won't have a front der. I would need a pretty serious chain tensioner such as a singleator or a rear dur stopped with a short backward cable. I have the gearing figured out where I will run a 20t freewheel in the rear and a 52 and 38 up front. I am pretty sure this will work if I don't get the chainline out of wack and can keep tension on the chain.
What have I not thought of? Suggestions, comments?