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Old 04-18-15, 02:18 PM   #1
jerky1280
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Shimano XT M771 Capacities

I'm planning to run a 10-speed setup on my tandem with an XT M771 9speed derailleur and a 105 5703 shifter in order to maximize my rear gear options (need to go both slow and fast). For the big mountains I'd like to run 54-42-30 in the front and a 12-36 in the rear. I'd be exceeding the 45T published chain wrap capacity of the rear derailleur by 3 teeth. I'd also be exceeding the 34T maximum by 2 teeth.

I've experienced that derailleur specs tend to be conservation (for example, I'm running a 42t sprocket on my mountain bike SRAM setup, which far exceeds the specs).

Does anyone expect a problem with this setup?
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Old 04-18-15, 03:03 PM   #2
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Three teeth above capacity should be very workable. As you note, there is fudge room in the specs.

Just be sure you leave the chain long enough to loop the big/big combination with room to spare (1" minimum). Worst case you run out of capacity and cannot take up the chain in the granny and smallest few rear sprockets.

Actually, my greatest concern is using a 30/36 combination on a tandem. That's an awful lot of weight and torque capability and if pushed hard up a steep wall may (may, not will) be more than the freewheel mechanism can handle. Of course this depends on how strong the riders are, how heavy and how steep, and there's no way to know until the bike tells you.

So go ahead, and just try to take it a bit easy on the steepest hills (if you can push a tandem up them anyway (they're murder to handle at low climbing speeds)
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Old 04-18-15, 09:24 PM   #3
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Thanks for the input. We're not a very strong team, which is why we need the low gears! I'm willing to take the risk. Right now we're running 24-27 on an eight speed setup.
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Old 04-18-15, 09:33 PM   #4
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Originally Posted by jerky1280 View Post
Thanks for the input. We're not a very strong team, which is why we need the low gears! I'm willing to take the risk. Right now we're running 24-27 on an eight speed setup.
Not an unreasonable decision, it'll buy you another step lower at the bottom end. I'm impressed that you can keep a tandem upright climbing in gears that low. I know people who have problems keeping solo bikes up at those speeds.
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