I tend to find that all to often people try to prescribe a universal, do it all, single speed ratio. I personally couldn't beg to differ more. I think that ultimately there are seemingly innumerable variables to consider when factoring in what ratio you will settle on at the end of the day, but i find that one of the most important factors remains the terrain that one rides on. Are you riding on loose gravel or hard pack with serious elevation fluctuation, or is your riding merely a short city commute where the tarmac is of immaculate condition and the hills are seemingly non existent. For city cruising i find a 36:16 ratio to be a great all rounder. With 1.9-2.1" wide semi slick 26" tires, i tend to find mostly everything the streets throw my way to be negotiable. When it comes to the irrigation ditches and single track in this area, i find that a 36:18 ratio works better when running 2.0-2.2" semi-knob treads. Another huge variable to consider is of course how fit you are, the overall weight of your rig, geometry, bicycle fitment, and your abilities as a rider or lackthereof to render the rocky terrain or city obstacles negligible. I noticed that to the degree that i ride with confidence and utilize the fruit of my previous experiences, i can to that very degree afford to ride slightly larger ratios. I still consider myself an amature when it comes to riding the various off road terrain that the city of Albuquerque, New Mexico has to offer, but when its all said and done i seem to gravitate toward the 36-38:18-16 range of ratio combinations for single speed riding.
(^_^)