What is a fixed gear bicycle and what is it for?

Question

What is a fixed gear bicycle and what is it for?

Answer 1

That was my only choice when I got my first bike.

Answer 2

A fixed gear bicycle is a bike with just one gear. It is used to train cadence (pedalling speed) on the flat and downhills, and strength on the uphills.

Answer 3

It's a bike with a single rear sprocket without a freewheel. All track racing cycles have them although road cyclists do sometimes use them also.  

Answer 4

Strictly speaking, it is a one-speed bicycle with no freewheel.  That means that if the rear wheel is spinning your legs must be moving, and vice versa.  You can even pedal backwards, which makes track stands very easy.  They typically do not have any brakes, and are slowed by a controlled slowing of pedal speed.

Fixed gear bikes ("fixies") are purpose built, and that purpose is racing on an closed velodrome track.  They have become popular with the bicycle messenger crowd because they are "tough" and "cool" but they usually install brakes, and often put a freewheel on the rear, which technically makes them not fixed gear at all.

I own a Bianchi Pista, which has a flip-flop rear wheel, fixed on one side and a freewheel on the other, which I ride at the local track in fixed configuration and around the neighborhood from time to time in the freewheel configuration.  You can see it in the second link below.  It’s a lot of fun, but I don’t attempt to ride it outside of the track in the fixed configuration, and I’ve installed a front brake.

On RAGBRAI last year there was an entire group of guys who rode all the way across Iowa on true fixed gear bikes.  The ones with whom I spoke regretted it, especially the absence of a freewheel.