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Discussion Starter · #1 ·
I have a Santa Cruz Highball with (new) SRAM 2x10 X9, and the chain jumps off of the crank ring when coasting over rough terrain. The result is disastrous when coasting into a dip, then getting out of the saddle to pedal up the other side, and the crank spins out from under me because the chain is not engaged on the crank ring. It doesn’t seem to matter what gear it is in, although I only use the small ring for long or steep climbs in the saddle, so who knows. Also, if I’m riding hard and fast, of course I’m in the smaller half of the cassette, so that’s going to be where it happens. It is not dropping down to the inside, so a chain keeper is not the answer. In fact, it doesn’t necessarily even jump all the way down to the small ring. It’s just disengaged. The front derailleur has been meticulously adjusted by two different professional mechanics. The chain length has also been confirmed by both of them, and it stretches the rear derailleur nearly to its limit when in the big ring/big cog combo. The last mechanic called both SRAM and Santa Cruz to confirm that the drive line and all other aspects of the setup were correct. Any other thoughts?
 

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Just a flesh wound
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Do you have a long cage or short cage rear derailleur? The take up you need for a 2 X 10 is such that a long cage might be too slack or have too much bounce in some gear combinations.

Measuring the chain by Derailleur "stretch" is not the right way to determine chain length. Big, Big plus 2 works really well. In big chainring and biggest cog, your Rear D will (should) look unhappy, or at least a bit stressed..
 

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I have the same setup, it happened to me a couple of times, I think the chain is a little bit long according to SRAM chain setup guide, just remove 2 links and the problem goes away, but then the chain look too sort when you are on big big combo. I've been ridding it this way for a few month with no I'll effect.
 

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Discussion Starter · #6 ·
Do you have a long cage or short cage rear derailleur? The take up you need for a 2 X 10 is such that a long cage might be too slack or have too much bounce in some gear combinations.

Measuring the chain by Derailleur "stretch" is not the right way to determine chain length. Big, Big plus 2 works really well. In big chainring and biggest cog, your Rear D will (should) look unhappy, or at least a bit stressed..
My rear der looks quite "unhappy" in the big/big and it doesn't help.
KN
 

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Just a flesh wound
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Chain line? I am reaching now. So it just drops off the chain rings when you hit bumps and you are not pedaling? Either big or small?

Maybe the front derailleur is not close enough to the rings? You know too high or something weird like that. Wish I knew the answer, but I think you'll have to send some pictures. Someone out here will know!
 

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Same issue.

XX 39/26 q166 cranks, Mojo HD, XX RearD, tried both X0 & XT FrontD

Shortening chain barely helped. Switching to a Shimano FD helped some but not much. I also added the MRP 2x guide so that eliminated the possibility of losing it off the bottom. It is falling off the top.

What I figured out is you must ride in the third or forth cog in back to keep the chainline straight. Then it stays on. That or don't stop pedaling. I think I'll be switching to a setup w/bash ring again unless someone comes up with a better solution.
 

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Shorten chain or derailleur cage, or obtain chainguide. Riding on big/big is bad luck, even if it's 'allowed' on 2x setups.
Sounds like we've all done the shortening and it didn't help much at all. A guide didn't solve the issue either cause its falling off the top, not just the bottom. Riding big - big runs smooth, so why would someone not use that gearing. Same with the reverse. Neither one is when this issue occurs. Shortening the chain to the point that an accidental shift into big-big gearing can rip the RD off the bike or break the chain would be stupid and that's what would happen if I took another link out.

Typically I lose the chain when I'm rallying in the big ring and one of the smaller cassette cogs just using a few pedal strokes here and there to accelerate out of turns at crazy fun speeds. Pumping through chunder and off jumps. Suddenly, I have no chain since it's wrapped outside the ring around the no longer pretty looking carbon crank arm. And yes, the FD is adjusted perfectly. Checked it 40 times at least and have tried two different brand FD's. :madman::madman::madman:
 

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On SRAM you have to remove a spacer from the Non-drive side to shift it, but not a bad thought. I'm down to only about 1mm already due to needing to space it over to work with the 2x guide. Hard to believe that 1mm more will solve it, but I made this quick change and will report back so this thread has more info.
 
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