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Almost every time I go from the big, to the small, front cog on my SRAM Red 2011 (with a KMC chain), the chain ends in the lower pulley position, as shown in the photo. Why? enter image description here

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Has it always done this? Or is it a new development? Is it possible that the derailleur cage or derailleur tab on the frame are bent? –  WTHarper Jul 1 '13 at 1:27
    
I second WTHarper; stop by your LBS and have your hanger alignment checked. –  Ken Hiatt Jul 1 '13 at 5:56
    
And, does it only happen for this specific change? Or can it happen at other times? –  PeteH Jul 1 '13 at 7:04
    
It should be noted that when happens it's very easy to bend the derailer or hanger as the chain hangs up and tries to rip off the derailer. –  Daniel R Hicks Jul 1 '13 at 15:37

1 Answer 1

Because you're cross-chaining -- creating a bad chain angle. With any dual derailer bike the chain angle is straighter if you use big front cogs with small rear cogs and vice-versa. And with bikes with lots of rear cogs the chain angle can get bad enough to cause this situation.

Basically you need to learn to avoid cog combos that create a bad chain angle, and, in particular, when down-shifting on the front you should generally be at least 2-3 cogs away from the smallest on the rear (given you have a 10-speed rear). (Keep in mind that you should tend to do this naturally if you're making good use of your gear range -- slowly shift down (larger cogs) on the rear as difficulty increases, then shift the front when you're fairly far "downshifted".)

In other words, don't try to muscle ups a hill in a high gear and then downshift with the front when the effort gets too much -- take it in steps.

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I know that cross chaining is "bad", but SRAM markets their yaw front derailleur and "True 22" system as allowing for such a setup. Is it possible that the OP's issue is simply an alignment and trim issue with the FD? –  Ritch Melton Jun 30 '13 at 21:20
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@RitchMelton -- It's possible that the problem is exacerbated by a misalignment somehow, moving the small front cog too far to the left vs the rear cogs. (And maybe the KMC chain on SRAM cogs is creating bad karma.) Keep in mind that a properly adjusted front derailer does not touch the chain when not actually shifting, and hence does not affect chain position. –  Daniel R Hicks Jun 30 '13 at 23:07
    
Chainlines can differ from build to build. Maybe it's possible that, while Sram allows for the chain to cross completely, it will pull the chain off of the tension pulley if the chainline is too far inward. –  WTHarper Jul 1 '13 at 1:26
    
Well, I had a crash, during a race Saturday... I'm ordering a new hanger (from Canyon), and see whether it solves the problem or not. –  T0TTE Jul 2 '13 at 6:22

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