At the ripened age of 59 (just) and having discovered the fixed gear road bike, the physical question is of course the gear ratio. After a couple of chain ring changes & cog replacements I have decided that a 39 X 16 feels pretty good. Fast rpm's but at 80 cycles per minute and at @ 20 mph I'm there. At a lower cpm I'm just cruisin. Lucky I'm limber (lucky I'm alive). The idea for such a low ratio is zero physical impact from the neck down...........Gear ratio input would be appreciated and hey, try a fixie.