A4 scale = 70%

Cycle transmission notes page 6

Successful rear derailleur indexing

Until the 1980's most gear shifters were of the 'friction' type and didn't have clicks in them; riders had to change their gears by feel and could only tell how accurately this had been achieved by listening carefully. Today rear gears are 'indexed', which means that the shifters can only click into pre-defined positions. Thus modern gears have to be setup far more accurately if they are to work properly and the different parts of the system - sprockets, rear mech and shifter - must be designed to work together.

Contrary to misleading claims made by both Shimano and Campagnolo, it is not necessary for every part of your system to come from the same 'groupset'. Just four requirements must be met if it is to index properly:

1. Your gears (your rear mech and shifter) must be matched, which usually means the same make and vintage, and they must be in good condition. Note, however, that you can use any make of rear freehub. (See the next page if you want to mix mechs and shifters from different manufacturers.)
2. Any inner and outer cable may be used as long as they are designed for indexed gears. They must be in good condition, free from kinks and move freely without passing round any tight corners. Squirt a little thin oil down all outer cables before assembly and on any cable guides such as those found under bottom brackets. And lubricate all the pivots in your rear mech while you're at it.
    
   

   If these 2 requirements are met then the pitch of your rear mech (the distance it moves for each click of the shifter, except the first one) is as follows:   rear mech and shifter (same make/vintage) pitch        7 sp   (all makes)          8 sp   (Campag, Sachs)            8 sp   (Shimano, SRAM)              9 sp   (Campag)                9 sp   (Shimano, SRAM)                  10 sp   (Campag)                    10 sp   (Shimano) 5.00 mm 5.00 mm 4.80 mm 4.55 mm 4.35 mm 4.15 mm 3.95 mm

    
   
3. Your rear sprockets must be evenly spaced by the same distance (called the sprocket pitch). So, for example, a 7 speed cassette will index perfectly with Shimano 9 speed gears, even on a Campag hub, so long as its sprockets are 4.35mm apart (2 clicks will be redundant).
4. The last requirement is that everything is correctly adjusted according to the instructions which came with your rear mech and shifters.

How many sprockets can I fit?

You may have to sacrifice a sprocket or two when using different makes of freehub and gears. The following table shows how many correctly-spaced sprockets you can fit to your hub:

( + :  add packing spacers before the largest sprocket )

© Chris Bell, 2006

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