On a
bicycle, the
gears and
chain are located on the right side of the bike by convention. This works wonderfully for almost all situations, except
BMX. Every rider has a dominant side, much like a
skateboarder. When
airing a ramp, for example, the rider's
dominant side will generally be the one facing the
coping as they turn, or the side on which they grind more
easily (many riders, for this reason, only run
pegs on their dominant side).
The problem arises with riders who grind right, which is apparently more common than grinding left (I grind left). Grinding on the side of the bike where the drive hardware is mounted is just inviting a broken chain, bent/chipped sprocket, or worse. In recent years, with the advent of cassette hubs (as opposed to the traditional freewheel system), manufacturers have addressed this issue by producing rear gears that ratchet in the opposite direction, and mounting the sprocket and chain on the left. This allows a right-side grinding rider more freedom in mounting a ledge or rail.