GS &
SGS are Shimano designations for their MTB cages -- essentially, Gran Sport & Super/(
Supra?) Gran Sport ... the designation originating with their CRANE (
CRANE was the precursor to the first generation of Dura Ace which were essentially the same EXCEPT for the use of bolts which used Allen Wrenches instead of having traditional, hex-headed bolt heads) rear derailleurs in the 70s (
pre-MTB).
The length of the LONG CAGE on all
off-the-shelf Shimano Road rear derailleurs is the equivalent of the MEDIUM CAGE on all of their MTB rear derailleurs.
In the past ~10 years, some of the SGS rear derailleur cages are now longer ...
The cage on most Shimano rear derailleurs can be swapped with the cage from another (the 950/952 rear derailleurs are exceptions which I know of because their cages are secured with a bolt in the same fashion as Campagnolo's Record/Chorus rear derailleurs) ...
AFAIK, there are no off-the-shelf SGS Road rear deraillerus ... but, because most of the cages were interchangeable in the past, it is possible to swap cages between Shimano rear derailleurs. Here is an Ultegra rear derailleur which I mated with an XT rear derailleur's cage ...
The Road rear derailleur with the SGS cage would be suitable when using a smaller-than-normal Granny on a Triple.
And, here is a
short cage Road cage which I attached to a "Rapid Rise" XT rear derailleur ...
My intent, FWIW, was to pair the particular rear derailleur with a set of Shimano Road shifters to facilitate what
I consider to be slow downshifting to larger Cogs when using a standard Shimano Road rear derailleur & a set of Shimano shifters!?!
That is (and, this comment is mostly for others who do not believe that "dwell" exists), Shimano did not call their reverse-pull rear derailleurs "Rapid Rise" because they thought it would be a clever marketing name.
FYI. I believe that you are correct that the bushing from your 11t Pulley Wheel will sleeve into the 10t Pulley Wheel. You just have to trust me that some DIY modification (
that is, the removal of EXCESS material) will need to be made to make it work ...
You will want to use the 11t Pulley Wheel's bushing (
you could theoretically file the longer bushing to the correct length) ...
This may be stating the obvious ...
Essentially, the Pulley Wheels which use bushings
float between the two "caps" while riding on the bushing ... Shimano seems to deliver the derailleurs without any lube of any kind on the bushings ... I think that any light grease is beneficial ....
My recollection is that the portion of the specific 10t Pulley Wheels which is below the "caps" is slightly raised so that they nest inside the "caps" to create a
labyrinth seal ...
Because I have not modified one, yet, I am not certain how well the 11t "caps" will fit after the excess material is removed ...
So, you will be sailing into unknown waters.
BTW. Shimano did make-and-use 10t pulleys between 1998-and-2001(?) which can be directly interchanged with their 11t pulleys ..
The XTR RD-M950 (for example) has 10t Pulley Wheels and the difference between it and the XTR 952 rear derailleur will be the 11t Pulley Wheels, the derailleur hanger BOLT (essentially a cosmetic change with the earlier bolt head being domed and the newer bolt having a stepped, concave head), and having "Mega 9" silk screened on the cage.
The XTR 950 rear derailleur was available with three different cage lengths with the shortest being the same length as the short cage Road rear derailleur & intended (AFAIK) for Downhill bikes which typically only have a single Chainring.
BTW. Campagnolo only changed to 11t Pulley Wheels about 5+ years ago; and, their 1998-present (
I think that their Xenon derailleurs are still being sold ... maybe not) 10t Pulley wheels are a compatible width ...
Campagnolo Pulley Wheels of any ilk cost more in the States ...
Also, Campagnolo uses a bolt whose outer diameter is incrementally (0.1mm?) smaller (the thread pitch is the same) ... I have not compared the bushing ODs, so I do not know how much DIY modification needs to be made..
That's an incredibly long preamble to say that I think you can
probably use an 11-34 Cassette if you change the upper Pulley Wheel (
as pictured in the earlier post) ...
But, your current derailleur's pulley cage will result in a
slack return chain when you use some combinations with the inner Chainring if you eventually replace the chain with one which is the proper length for the Big-Big combination ...
Although MY chain was long enough so that the "ideal" length chain for a 12-26 & 53/39 combination could theoretically be used with the 39t Chainring & 34t Cog, YOUR current chain may-or-may-not be long enough ...
So, while you can probably use your current combination with a MTB Cassette whose largest Cog is as large 34t, then when the time comes for you to buy a new chain, you should make it long enough for the Big-Big combination BUT, you should get a new chain
GS cages may-or-may-not be hard to find on most current Shimano rear derailleurs without placing a special order ...
Since I am not racing, there is nothing wrong, IMO, with dragging the few extra links which an SGS cage can accommodate.
FYI. I
love the 950/952 rear derailleurs, but I definitely recommend the XT 750 (
why pay more?) because of the relative lack of derailleur cage interchangeability with the XTR rear derailleurs ...
And, the difference in price between a 'vintage' XT rear derailleur and a lesser Shimano MTB rear derailleur is usually negligible.
The Sora, Tiagra, and 105 rear derailleurs which you indicated would benefit for the 10t upper Pulley Wheel swap ...
The LX, XT, and XTR should are probably good-to-go without swapping the upper Pulley Wheel ...
I am NOT certain about the Deore RD-510 whose parallelogram may be the same "short" length used on Shmano's Road rear derailleurs; so I would treat it like a long cage Road derailleur which may require a 10t Upper Pulley wheel which Shimano's Road rear derailleurs need when mated with MTB Cassettes which have larger Cogs.