I want to improve the front shifting on my wife's road bike, which has an RSX compact triple
46-36-26. The frame is a 1997 Giant TCR, with a bolt-on bracket for a braze-on dérailleur. I'm
currently using an RSX eight speed braze-on FDR, but there doesn't seem to be enough range - i.e. if
I have it set so that it will just shift down to the granny, the chain rubs in the large ring. If I
tighten the cable so that the chain clears the FDR in the large ring, it won't shift down. (FWIW,
the shifters are nine speed Shimano 105 model ST-5510, and the bike has a nine speed
cassette/chain).
So I'm considering trying a Deore dérailleur - preferably the top swing version so that the clamp
will be below the bolt holes/water bottle mount on the seat tube. The seat tube is about 1 3/8"
diameter, so I can remove the bolt-on bracket and use a 34.9mm clamp-on.
But there's a spec difference - the bottom swing version of the Deore FDR is spec'd for 44/46/48
large ring - the top swing is spec'd for 44 only. I have a gut feel the top swing'll work with a 46
anyway, but I'm curious as to why there's a difference in the spec. Does anyone have any insight?
Thanks