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Does anyone know whether one of Shimano's new "direct pull" rear mountain derailleurs, like the RD-M591 or RD-M770, will work OK on a road bike setup? I'm concerned about the cable routing, which eschews the traditional rear-facing loop of other derailleurs.

I'm considering putting an 11-32 on my road bike with a compact front setup (50/34, already on the bike), for climbing mtn. passes in CO. Please no comments about HTFU, real men just blow out their knees, etc. I have good reasons for considering this setup.

Alternatively, can anyone vouch that a long cage Shimano road RD could handle the 32T rear cog? If so I'd be interested in knowing which one works. I know Shimano only specs out to 27T, but Sheldon Brown and others say you can exceed that "by a few teeth."
 

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I used a Deore long cage RD with both old Ultegra 600 and Sora 8-speed shifters combined with a 50-34 crank and 12-30 cassette. Shifted well enough, but the chain was really l-o-n-g. It worked, and any shifting messiness, I attribute to my low quality Nashbar compact crank.

Got my old, heavy bike and aging body up the hills, you know.
 

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The short cages can go up to 28t in the back, and I've heard of many who have used long cage derailleurs with 32t cogs successfully.
As for the MTB derailleur, I can't answer it for you.
 

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Those derailleurs are 9sp and look to have standard cable routing. They'll work with road shifters. It's the 10sp ones that don't. Make sure you get high normal not low normal.

Road triple RDs can handle a 30t cog but 32 is pushing it. Some people have turned the B screw backwards to get a bit more room or replaced it with a longer screw.
 

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old school drop out
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The cable pull ratio on the new style mountain deraillers is the same as the old style, so yes they will work However, depending on the specific design of your frame, there could be issues with cable routing (but it's very likely to work fine).
 

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I've run XT rear mechs on three different cross bikes...9 speed and 10 speed. There are no issues. The shifting is perfectly fine. The XT shortcage actually shifts better than a road r/d! The pivots are stouter and the spring is heavier.
 
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