Two professional bikers are biking at the Peckham BMX Club.  The bikers are going over a curbed surface at full speed.  There are several other bikers doing the same activity on another curved surface.  There are five bikers wearing helmets standing ready to start a race.  They begin racing at high speed over a curved road.  Two more batches of racers start the same race.  A single biker is going through the curved road at very high speed.