Derailleur Gears; Derailleur Gears - How They Work And How To Operate Them On Mountain, Cruise And Touring Bikes - BMW Mountain Bike Enduro Owner's Manual

6.2 Derailleur Gears.

Derailleur gears are currently the most effective type of power transmis-
sion on bicycles. With specially designed sprocket teeth, flexible chains
and indexed lever positions, gear shifting has become very easy. Some
systems have an indicator on the handlebars showing the currently used
gear.
Modern mountain and touring bikes can have up to 27 speeds. It is not
advisable to use gears which involve an extremely oblique run of the
chain, as this reduces power transmission efficiency and hastens wear of
the chain. An unfavourable run of the chain is when the smallest chain-
ring is used with one of the two or three outermost (smallest) sprockets
(a)
or when the largest chainring is used with one of the inmost (largest)
sprockets (b).
Always wear straight-cut trousers or use cycle clips or the like
(c)
to make sure your trousers do not get caught in the chain or
chainrings.
Shifting gears under load, i.e. while pedalling hard, can make
the chain slip. At the front derailleur the chain may even slip off
the chainrings and result in an accident.
At least the durability of the chain will be shortened considerably.
a b
6.2.1 Derailleur Gears – How They Work and How to
operate Them on mountain, cruise and Touring Bikes.
Gear shifting is initiated by actuating a shifter, a combined brake and
gear lever unit or by a short turn of the wrist with the twist grip, as the
case may be.
With Shimano Rapidfire Plus shifters pressing the large shifter moves
the chain towards the larger sprockets. Pulling the small lever, located
in front of the handlebars from the rider's viewpoint and operated with
the index finger (index finger lever) shifts the chain towards the smaller
sprockets. This means that any gear shift made by pushing the large
thumb shifter on the right produces a lower gear, while pressing the
large thumb shifter on the left moves the chain to the larger chainring,
thus producing a higher gear.
The Shimano Rapidfire Plus shifters with 2-way release
XTR from model 2007 on) work according to the usual Rapidfire prin-
ciple (see above). The small index finger lever can be operated with the
thumb, as well. The chain runs to the small chainring or small sprockets.
You can shift several gears with one action. Pulling or pushing the shift-
ing lever shortly results in a single gear change, pulling or pushing it long
leads to two gear shifts.
Shimano Rapid Rise derailleurs use a return spring with reversed
spring direction. Shifting with this derailleur is reversed from common
derailleurs, i.e. actuating the big shifter with the right hand leads to a
higher gear.
c
(d)
(e.g.
d
29