The one-speed revolution actually involves two different styles of bikes, singlespeeds and fixed gears. Fixed-gear fans like the late bike mechanic and writer Sheldon Brown tout the simplicity, feel and efficiency of the bikes; while detractors often prefer the mechanical advantages of derailleur bikes and the fun of coasting.
Riding a fixed gear bike is just fun! In a way, it's like learning to ride a bike all over again and experiencing the subtle joys of discovering an efficient way to get from here to there with a lot less energy than walking or running. In order to understand the benefits, you have to look past the negative stigmas of the lifestyle, personalities and misconceptions that often get associated with it, and just see it for the healthy activity that it is. You can slow or even stop your fixed-gear bicycle without the use of separate brakes, by forcibly slowing the movement of the pedals. Climbing and descending your favorite hills becomes a new challenge, and the fixed gear adds a new dimension to your familiar terrain.
Fixed gear is not ideal for all circumstances, however.
Beyond the basic pleasures of using of a fixed gear, numerous articles by respected coaches and professional cyclists recommend the benefits of using a fixed gear not only for enhanced training and efficient use of your training time, but also for the added variety to a rigorous road training regimen. You don't realize how much mental energy you devote to shifting until you relinquish your derailers, and discover that a whole corner of your brain that was formerly wondering when to shift is now free to enjoy your surroundings and sensations.
With my singlespeed, I can put all my force into acceleration and not ever worry about my chain breaking or skipping.
A singlespeed bike dispenses with the weight of the derailers, shifters, cables, extra sprockets and longer chain.
You don't have to choose once and for all between fixed and freewheel, because the same bike can be both, if you use a reversible "flip-flop" hub. With a fixed gear you simply have a frame, cranks, pedals, cogs, chains and wheels.
The gears may also be thicker, which results in more durability and longer drivetrain life.
I STRONGLY recommend starting out with fixed gear.
Problems
If you ride in a hilly area, you may find that riding a fixed-gear bike puts too much strain on your knees. While riding a rolling course, work on being comfortable with a very high cadence on the downhills and keep your heart rate in check on the climbs.
Optimum pedaling cadence is different for every rider.but my bet is you won't want to if you give fixed gear a good try (typically takes a couple of weeks of regular riding to get past the strangeness, but then it's quite addictive!)
Most folks who set up their bikes with a fixed/free flip-flop wind up using the fixed gear side pretty much all of the time. Many riders also swear by the amount of control a fixie offers. Olen advises that you to keep your chain well oiled and expect to have to replace your rear tire more frequently as a result of skid stops.