used 6KU Aluminum Fixed Gear Single-Speed Custom Urban Road Bicycle. 700c wheels Flip flop 24 inch frame Hand brakes front and back Handlebar extension for more relaxed ride! Urban Track has a lightweight aluminum frame and fork. Track Frames are made of lightweight 6061 aluminum with easy to touch welding. The Flip Flop Hub gives Track Bikes a thing, whether you ride a fixed gear or a pedal.