Gear Combo Guru
Join Date: May 2007
Bikes: Spec' Tarmac (road), Ridley Fenix (commuter & fast tourer), Salsa Mamasita (MTB), CoMo Speedster (tandem), Surly Big Dummy (cargo), Airnimal (folder)
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I got a good deal on an XTR rear derailleur recently, and so I decided to put it on the tandem instead of the XT that we'd been using for half a year (the XT went to another bike that was in need).
I was very disappointed with the XTR. We have a BIG gear range, which is why I need a MTB RD, but the cage on the XTR is about 1 cm shorter than on the XT. Also, to save weight, the XTR RD doesn't have a cable tension adjuster, which is something that I always use (I put an adjuster on the frame's cable stop near the handlebars, but it doesn't have a huge range, and so I prefer to leave that in the middle and save it for on-the-road adjustments). The one thing that I did like about the XTR is that it is advertised as having a stronger return spring than other RDs, which I thought would be a good thing given the length of the tandem's shift cable and slightly odd routing. This seems to be an improvement, but overall I regret not simply getting another XT rear derailleur.
We also had an Ultegra RD on the bike before changing lots of things, and it worked fine (it just didn't have the chain-wrap capacity when we switched to a quad chainring setup). The gearing setup that you describe would be at the edge of the Ultegra's limits, but it should still work OK (as long as you avoid the small-small combos). If I was choosing any RD for this setup though, I would go with the XT - it really doesn't seem to have any drawbacks or limitations, and is the most versatile (and don't worry, 10-speed is not a problem for it).
Last edited by Chris_W; 09-21-09 at 03:00 PM.