Choosing a rear derailleur

zcacogp

Chaps,

The rear derailleur on my bike is past it. It's a bit mangled (always has been as I bought the bike cheaply second-hand) and, when cleaning and lubricating the chain yesterday, I also noticed that it's not in line with the rear cogs (one side of the 'cage' drags on the chain) and that the bearings on the parallelogram mechanism are worn such that there is quite a lot of play in the whole thing. I adjusted it, but I think it's time to think about a new one.

The snag is choosing which one to buy. The bike is an old Claud Butler Chinook, with a 'Shimano 2300' rear mechanism (or so an on-line description tells me). It seems that the general advice is to replace kit on a like-for-like basis so I need another Shimano rear derailleur. The 2300 is no longer available and there are eight cogs on the rear wheel so I think I need another Shimano rear derailleur that will work with eight speeds. Everything now seems to work on 10-speeds, but there is this at Wiggle:

http://www.wiggle.co.uk/shimano-altus-m ... erailleur/

(It's a Shimano Altus 7/8 speed).

Will this work? Is it any good? What other options are there which would also work? The handlebars have thumb-push gear change mechanisms so whatever I get will have to work with them, unless I change those as well (which I'd rather not have to do).

All help welcomed - thanks!


Oli.

dgmoose

The model number of the rear derailleur will be stamped on the underside of the parallelogram and should be something like RD-xxxx.

It sounds like you have the inexpensive Shimano indexed shifters that are mounted on the flats close to the stem which operate just like downtube levers or barend shifters.

As far as cable pull compatibility goes, any model of Shimano derailleur designated as for Road 7, 8, 9, 10 speed (but not RD-4700) or MTB 7, 8, 9 speed will work. But, keep your choice to 9 speed or below since the pulley wheels may be too thin for the wide 7/8 speed chain.

Also, you need to calculate the capacity requirement of the replacement derailleur:

C = (biggest chainring - smallest chainring) + (biggest cassette cog - smallest cassette cog)


Capacity is the derailleur's ability to take up chain slack and this is related to cage length. So, you need a derailleur with a designated capacity equal to or higher than the one you calculated above.

zcacogp

dgmoose,

Thanks - that's really helpful.

I've had a closer look at the bike and the rear derailleur is stamped "RD2200 Shimano Singapore" in the position you mentioned.

The shifters have a sticker on the bottom of them saying "ST-R221", and look like this:



(Obviously, the one of the other side only has 3 positions).

I've counted the teeth on the front and rear chain sprockets.

Rear cassette is 8-speed, from 13-26 (difference = 13).

Front chainring is 30-52, giving a difference of 22. However I have never used the smallest chainring and the middle chainring is 42. Should I therefore use a difference of 10?

This gives C=35 (or 22).

Which derailleur should I buy?

Thanks again for your help.


Oli.

The Rookie

dgmoose wrote:

But, keep your choice to 9 speed or below since the pulley wheels may be too thin for the wide 7/8 speed chain.

Given that the internal width of 7-10 speed chains is all the same at 3/32”, then a 10 speed will work just fine.

svetty

zcacogp wrote:

Which derailleur should I buy?
Oli.

The one you linked to should be fine

dgmoose

The shifter pictured is a combo lever.

The rear derailleur that you linked is compatible.

Shimano's nomenclature for derailleur cage lengths are:

SS = Short cage
GS = Medium cage
SGS = Long cage

For some Shimano derailleurs 35T capacity would be short cage (SS), however, older SS models had 29T capacity with 37T being GS medium cage.

Therefore, erring on the side of capacity compatibility, any of these models (although not exhaustive) in either GS or SGS cage lengths will work:

Road rear derailleurs: RD-220x, 230x, Claris (240x, R200x), Sora (330x, 340x, R300x), Tiagra (440x, 450x), 105 (550x), Ultegra (650x), ... where x is usually 0 or 1.

Commuter/MTB rear derailleurs: Altus (RD-M310), Acera (M330, M370), Deore (M51x, M53x, M59x), LX (M56x, M57x, M58x), SLX (M66x), XT (M73x, M75x, M76x, M77x), XTR (M95x, M96x, M97x),... where x is usually 0, 1, or 2.


Just choose one that suits your pocket and/or aesthetic preference.

The Rookie

dgmoose wrote:

Shimano's nomenclature for derailleur cage lengths are:

SS = Short cage
GS = Medium cage
SGS = Long cage

Actually Shimano call long cage GS, and super long SGS, there is no medium cage in Shimano nomenclature, only in common parlance.