new rear deraillier

[newbootclimbco]

I'm about to fit a new 11/34 cassette plus chain to my cannondale synapse from a 11/30 the existing rear deraillier is 2 and a quarter inches from centre to centre between the jockey wheels. with the larger cassette what size hanger should I fit.Thanks T.

[Brucey]

what

a) exact model RD and
b) chainrings

do you have ?


cheers

[newbootclimbco]

sorry Brucy, what do you mead by RD, cassette is a 10 speed.

[reohn2]

Rear Deraileur

[Brucey]

RD = rear derailleur

Need to know what chainring sizes you have because this affects the required total capacity of the RD

cheers

[newbootclimbco]

cheers,i'll post a reply tomorrow. T

[newbootclimbco]

Extra info regarding the above, At the moment the rear hanger is a shamano 105 2.1/4inches between centres of jockey wheels,front crank is a two piece 50/34. New cassette will be a 10 speed 11/34 and new chain. so what new length deraillier will I need. Old cassette was a 10 speed 11/30. Cheers T.

[Brucey]

the RD will have a model number on it, and there are two versions SS (short cage) and GS (longer cage). It will (I think, from your description) either be RD-5700-SS or (more likely) RD-5701-SS


RD-5700-SS has a max sprocket of 28T and a total capacity of 33T (cf GS version which has 28T and 39T)
RD-5701-SS has a max sprocket of 30T and a total capacity of 34T (cf GS version which has 32T and 40T)

The total capacity is the front difference eg. 50-34 = 16T plus the rear difference eg. 11-30 = 29T e.g. total capacity of 35T in this case.

Shimano are conservative about their specifications so you can (with a bit of careful setup) expect to go ~+2T without coming to grief, which presumably explains why your current setup (which uses +1T total capacity if you have RD-5701-SS) works at all.

But for RD-5701-SS with 50-34 (16T) and 11-34 (23T) you are exceeding the max sprocket size by +4T and the total capacity by +5T.

A longer gear hanger will solve the former issue but it won't solve the latter; this means that you will either have to set the chain so short you won't be able to use the 50/34 combination (dumb idea BTW, you are only ever one thoughtless shift away from breaking your bike) or accept slack running in the 34/(small sprocket) gears (better but still not advisable if there is an alternative).

An easy solution to this might be just to buy RD-5701-GS; this will probably work OK because you are only going +2T on max sprocket size. IIRC it is sometimes necessary (on some frames) to fit a longer B tension screw to make it work. Other times its usually just a question of setup.

cheers

[shobo]

I have a medium cage 105 RD ( RD-5701-SS ?) with a 32t sprocket, it works fine, I'm gonna try it with a 34t i suspect it might still be ok. At the same time change out my 52-36 with a 50-34.

[gxaustin]

I have a medium cage 105 RD ( RD-5701-SS ?) with a 32t sprocket, it works fine, I'm gonna try it with a 34t i suspect it might still be ok.

I think the medium cage is a GS

[Tiberius]

I think the medium cage is a GS

It is and it works fine with an 11-34 cassette...at least mine does.

[Brucey]

shimano are slightly inconsistent about what they call SS, GS, SGS. In different models of derailleur one can look much like a different sort. So 'short' 'medium' and 'long' are perhaps relative terms only, not absolutes.

cheers