Stolen from Surly's site:
The Steamroller is designed as a fixed gear street bike that’s track legal. We offer it up as a fixie with a Surly cog and lockring, but the rear hub is our fix/free, with fixed gear/lockring threads on one side and single speed freewheel threads on the other. There are no housing stops for a rear brake, which you’ll probably want if you decide to run it with a freewheel, but we include a front brake and lever regardless because fixie-pure or not, a brake helps keep you safe so you can spend your time on the bike instead of in the hospital.
It’s tough, the handling is snappy, the acceleration zippy, and it’ll take even bigger tires than we spec’d because big tires flex before the frame so they’re more comfortable and stay connected to the ground better than high pressure skinnies.
Whether you’re a neophyte looking to try ‘fixed,’ a seasoned messenger, a hipster, wonk, geek, freak, neo-zoom dweebie, or just want a simple, practical, long lasting, general-use single-speed, the Steamroller answers the call.