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I have a road/cyclocross/commuter frame that is currently spec'd with road components - all Shimano 105, with an Ultegra rear derailleur.

The cassette (10 spd) tops out at 27 teeth, and the rear derailleur has a very short cage compared to Deore/XT/XTR I've looked at. If I wanted to use a cassette with more teeth, 32 or 36 - I was wondering if there'd be any issue with swapping out the current Ultegra for a 10 spd Deore/XT/etc cassette & derailleur but still using the 105 STI? Both shifters & derailleur would be 10 spd, but I don't know if say cable pull is the same?

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2 Answers 2

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Won't work. Dyna-Sys uses a different pull ratio than Shimano road components, and the cassette uses a slightly different spacing as well. You could use a SRAM cassette, but that still leaves you with the derailleur issue. They do make 105 and Ultegra long cage derailleurs, however. If you've got a double up front, especially a double with proper cyclocross gearing (tigher ratio than standard or compact road), the long cage road derailleur should be more than adequate.

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It's a 50/34 - that's compact road, right? –  OMG Ponies Oct 23 '11 at 23:03
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Yup, that's compact road. You should be able to get away with an 11-32 no problem with a long cage road derailleur. As for a 34 or 36, well that's where your local bike shop becomes invaluable. Any decent shop that has said derailleur in stock shouldn't have a problem slapping one on to see if it will work out. If you're lucky one of the mechanics will have experience with the setup and be able to tell you one way or the other. Just don't use their time and knowledge and then walk out the door and buy online :) –  joelmdev Oct 23 '11 at 23:53
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+1 for getting help from your LBS. I've bought a cassette from my LBS and it didn't work with the derailleur. They couldn't even figure out why. But because I bought the cassette, took it home and fitted it they couldn't give me a refund. If they fit it, they'll probably wear the cost of components they try out. –  Mac Oct 24 '11 at 0:56
    
FYI. This is only a compatibly issue with 10-speed mountain gear. The new dyna-sys (deore / xt / slx / sgs ) changed the indexing ratios on the rear derailleur. The 9 speed road shifters and mountain derailleurs worked fine together. –  Benzo Jul 23 '12 at 19:42

I have heard that it can be made to work with a 9 speed MTB derailleur rather than a 10 speed; see here for a description of how.

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Whilst this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference. –  Gary.Ray Oct 24 '11 at 13:05

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