On 1 Oct, 18:59, "Graham" wrote:
"thirty-six" wrote in ...

On 1 Oct, 15:54, "Graham" wrote:

"AMuzi" wrote in ...

Ah well, there's none so blind as those who don't want to see.

perhaps someone else might like to help to point out there is a GS
(long arm) and an SGS (longer than long) *pulley-cage and only the sgs
cage is stated as suitable by the manufacturer for the gear range
Graham has quoted..

What I quoted was:

*Shifters - Shimano dura ace 10 speed STI, front mech - Shimano dura ace, rear mech - Shimano XTR M971, cassette - SRAM 10 speed 11-32 , chain - KMC 10 speed and chainset - FSA compact 50/34.

What you advised was:

type GS has a total capacity of 37 teeth, one can generally push the
large sprocket size but not the total capacity as this is set by the
cage length. *If it's the SGS then you should be able to make it
work , but make a positive identification before further testing,
adjusting and bashing it about.

So by my reckoning (50-34)+(32-11)= 37 total capacity. Just at the limit of the GS. So armed with your advice I did not think it necessary to worry about which model it was. Having now studied carefully the tech doc Andrew posted the link to it actually says 34 for the GS limit so I guess your 37 was a typo which I guess you did not "see".

I made that mistake, an unfortunate rework on my intended post led to
some inappropriate editing with transposed value.


My experience with road mechs indicates Shimano are very conservative over their capacities. I have the same chain ring and sprocket set up working smoothly with an Ultegra short cage with the B screw wound fully in. The cage on my friends XTR is way longer than the Ultegra and it was no where near the limits of travel on either big/big or small/small combinations.

Anyway just in case others advise that the capacity of Shimano mountain bike mechs is more critical than their road mechs and would have the effect on shifting performance I have described I have emailed my friend asking him to confirm which model he has. He has already taken his bike home and was happy with its shifting performance although after riding it for a while he might be back!


One can push the largest sprocket size but AFAIK one cannot push the
total-capacity and any derailleur will offer improved performance if
this capacity is shied away from.