All Mountain Bike Parts Descriptions
and Rear Derailleurs - The mechanical devices
that move the chain side to side.
The Front Derailleur, located above the crank,
pushes the bike chain side to side using two steel plates
(usually made of steel for durability). It also acts
as a chain guide, helping keep the chain going over
rough terrain. Most Front Derailleurs are clamped
to the bike at the seat tube, and some are fastened
to the bike on a bracket around the Bottom Bracket.
The Rear Derialleur, located below the
cog set on the rear wheel, guides or "derails"
the chain side to side under the cogs to get your
higher or lower gears. It also acts as a spring, pulling
back on the chain as it changes gears which, as well,
changes the chains length. The extra chain is soaked-up
between two pulley wheels below the main spring. Because
the Rear Derailleur sticks out the side of the wheel,
it is common for them to be impacted on, wacked by
closing doors (in apartments or houses), or rocks,
or totally crumpeled up into your rear wheel from
something jammed in your chain or a bent dearailleur
hanger. These mishaps are not covered under warranty
so be careful how you lay your bike down. Most aluminium
frames use break away pieces hangers on the Rear Derialleur.
They are designed to break first if you derailleur
gets snagged, hopefully saving it. They are also soft
and tend to bend causing out-of-sinc shifting. If
you want to check the alignment of the Rear Derialleur,
it's easier to see if you are standing behind the
bike. The two pulley wheels should be directly below
the cog. If they are not, you get to discover two
new friends "skip" and "spoke-wedgy".
Bike Parts Diagram