Originally Posted by
TejanoTrackie
A rear brake is unnecessary on a fixed gear, however, it doesn't hurt to have one. It does provide a degree of redundancy in the event your chain comes off and you are unable to brake your rear wheel with your legs. Needless to say, you should always have a front brake on any type of bike that is ridden on the road.
I agree completely.
A few things to consider...
Some laws require a front and rear brake that can "skid the tire." If you're concerned with such things or have local law enforcement that cares, then you might need a rear brake.
If it's really hilly, a back brake might be useful. Sure you can back pedal, but that's a weird force on your knees.
If you ride a road bike, you may want a consistent interface across bikes, that is two brake levers that actually do something rather than just one lever or two levers where one is a dummy.
And I agree with Bandera above. A true track geo frame is not comfortable or practical on the most metro area roads that are beat up with cracks, patches and potholes.