In article <[email hidden]>, Graeme Beech
Quoted message said:I am refurbishing a 1976 Raleigh Record Ace and need a new rear mech.
The chainwheels are 52/42 and the new cassette I'm buying is 13/30 - hub spacing problems have been
sorted out! Rear mech requirements are thus capacity 27, max sprocket 30.
Shimano rear mechs have capabilities as follows SGS type: capacity 43, max sprocket 34 GS type:
capacity 37, max sprocket 27 SS type: capacity 29, max sprocket 27
Thus I appear to need the SGS type by virtue of max sprocket size; however the SGS is a large
mountain bike mech which I would prefer to avoid.
It'll work fine, there's no strong reason to avoid it. Shimano MTB derailleurs are routinely used on
road bikes, every day. The MTB design is also superior for use on very wide spaced clusters due to
the angle of the parallelogram - your cluster has much bigger jumps than any that the SS/GS
derailleurs were designed to run on (12-27 being the largest Shimano road cluster).
Quoted message said:Will I be able to use a GS type despite the apparent max sprocket , bearing in mind its large
capacity (37) compared with my requrements
(27).
Probably/usually yes.
The GS type will often do 30t OK - since your front chainring difference is pretty small, you can
usually eke a little extra cog clearance in back by running a slightly shorter chain (ie, there's
a little extra chain tension when in low gear). Make sure it can still clear the big/big
combination though.
How well it works also depends on the shape of the derailleur tab on the frame.
--Paul
