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Discussion Starter #1
Just got a Stumpy FSR 29er (first FS bike!) love the bike but when cranking on high speed down hill runs the chain has a few times popped off the top gear down to the low gear causing almost death as my balance was thrown off.

Its a sram x7 front with a x9 rear and x7 shifters and GXP crank-set. I don't believe it is an adjustment issue as under "normal" operation there is never a problem. I don't seem to have any rubbing on the guides either. It only happens when I am in top gear (smallest ring in back, large ring up front).

Question.
Is it an adjustment issue anyway?
Is it because the chain is 'unloading' when hitting bumps at high speed while cranking?
Is it that I just need to get a chain guide?
Is this a FS bike problem with the chain not able to hold on under high speed compression on the rear?
Is it something else?
 

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Carbon & Ti rule
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subspd said:
Just got a Stumpy FSR 29er (first FS bike!) love the bike but when cranking on high speed down hill runs the chain has a few times popped off the top gear down to the low gear causing almost death as my balance was thrown off.

Its a sram x7 front with a x9 rear and x7 shifters and GXP crank-set. I don't believe it is an adjustment issue as under "normal" operation there is never a problem. I don't seem to have any rubbing on the guides either. It only happens when I am in top gear (smallest ring in back, large ring up front).

Question.
Is it an adjustment issue anyway?
Is it because the chain is 'unloading' when hitting bumps at high speed while cranking?
Is it that I just need to get a chain guide?
Is this a FS bike problem with the chain not able to hold on under high speed compression on the rear?
Is it something else?
It is adjustment,move the front derailer out a touch with the cable adjuster.

The reason it doesn't happen in the other gears is because the angle of the chain makes it closer to the inside of the deriliuer so when the chain trys to jump off the derailiuer guides it back on.

Had the problem on my rip9 & this sorted it.
 

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Sugary Exoskeleton
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Many/most FS bikes can do this when ridden hard on rough terrain even when the drivetrain is 100% perfect. The chain bounces around enough and eventually the movement "whips" the chain off the big ring from underneath. Under normal conditions or single hits the rear derailleur cage spring is strong enough to keep the chain under control.

It sounds like you are a candidate for a 2 ring chainguide. Blackspire Stinger and eThirteen Heim 2 mount easily and solve the problem 100%.

JMH
 

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Is your 2x system a conversion, as in did you just remove the biggest ring? If so Check your chain length too, if you converted from 3 gears in the front and did not shorten the chain you prob have to much slack going on in there. If it is not that it could also be a bb spacing issue if your running a true 2x system. Riding in your too biggest rings at the same time puts alot of angle on the chain and would make it more likely to fall off in the bumps. A real 2x crank should be able to handle this though I believe. If you have room to space in the BB or lessen the spindle length with a different crankset it might solve the problem, by decreasing that angle.
 

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Discussion Starter #6
It is a true 2x10 conversion. I think it may be time to try shortening the chain. Or I may need a chain guide. LBS is looking at it today to let me know their thoughts. Only does it when in the big front ring and smallest rear ring. (top gear) could just be chain unloading.
 

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I'll be psyched to hear what the shop says. I'm having the same issue on my 29er Epic. I've taken links out of the chain, adjusted the cable tension and limit screws and still the chain drops. Other threads are claiming it's an issue with spring tension being too weak in the rear derailleur. My tension seems fine, but I'm waiting to hear reports from others to see if that helps. Some folks are claiming that SRAM is offering replacements.
 

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mtroy said:
Shorten your chain.
+1


you size a chain by wrapping around the two largest gears, and bypassing the derailleur, then adding 2 links to that and then install the chain as normal through the derailleur... if you've already done this, try taking out one link... when in largest sprocket and largest chain ring, you can look at the rear derailleur jockeys and see visually if you're chain length is adequate or too long...
 

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Discussion Starter #11
LCW said:
+1


you size a chain by wrapping around the two largest gears, and bypassing the derailleur, then adding 2 links to that and then install the chain as normal through the derailleur... if you've already done this, try taking out one link... when in largest sprocket and largest chain ring, you can look at the rear derailleur jockeys and see visually if you're chain length is adequate or too long...
If it wasn't fixed I'll give this a try.
 

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FWIW, I've always gone by the rule that when you're in the largest chainring and the largest cog in back, the chain should still roll and not over/hyperextend the rear derailleur (which could break it). I've taken one link out of my chain, but if I take one more out, I won't be able to shift into that gear (which, on a 2x10 shouldn't be an issue- you should be able to use all gear combinations, though small-small makes little sense). I'm still getting the chain drop.

Lemme know if I'm wrong on this...
 

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transmitter~receiver
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alshead said:
FWIW, I've always gone by the rule that when you're in the largest chainring and the largest cog in back, the chain should still roll and not over/hyperextend the rear derailleur (which could break it). I've taken one link out of my chain, but if I take one more out, I won't be able to shift into that gear (which, on a 2x10 shouldn't be an issue- you should be able to use all gear combinations, though small-small makes little sense). I'm still getting the chain drop.

Lemme know if I'm wrong on this...
Having enough chain to not rip your derailleur off in big-big is an idiot-proof safety protocol.
It makes some sense on a basic level, but is unecessary if you aren't in the habit of cross-chaining severely.
The big-big combination makes as little sense as small-small.
 

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Thanks- just seems like you're not really "cross-chaining" when you've only got two up front- the big chainring is only a 36- comparable to most 34t middle rings...
 

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alshead said:
Thanks- just seems like you're not really "cross-chaining" when you've only got two up front- the big chainring is only a 36- comparable to most 34t middle rings...
You're right... it probably is less severe than cross chaining on a 3x set-up (don't know the 2x chainlines), but the gearing overlap means you can get the same ratio with a better (more efficient and reliable) chainline.
How does it make any more sense than small-small?
:thumbsup:
 

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My new 2x10 Sram XO equipped FS carbon 29er (Superfly 100 Elite ) has the chain fall off to the inside often, usually while negotiating tight, technical terrain with moderate speed while in the big ring. I believe it's due to the rear triangle flexing/twisting laterally. The der is adjusted properly, from what I can tell. When the chain drops, it doesn't hit the smaller ring, it gets stuck in no mans land freewheeling along the inside of the big ring, and rubbing on the front der, which is still in the correct position. Very annoying.
 

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CDB said:
My new 2x10 Sram XO equipped FS carbon 29er (Superfly 100 Elite ) has the chain fall off to the inside often, usually while negotiating tight, technical terrain with moderate speed while in the big ring. I believe it's due to the rear triangle flexing/twisting laterally. The der is adjusted properly, from what I can tell. When the chain drops, it doesn't hit the smaller ring, it gets stuck in no mans land freewheeling along the inside of the big ring, and rubbing on the front der, which is still in the correct position. Very annoying.
sounds like your front d. is not adjusted correctly.
 

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I agree that it does seem to be positioned improperly, based on the symptom and occurring frequency of the drop. Except... I will say that if it is positioned any further outboard, it freely drops to the outside (already doing so, just as often). Vertically, der is positioned so the cage clears the big ring teeth by no more than 2mm, which is normal. The face of the cage is parallel to the chainring plane (direct mount). Carbon cranks have gotten really trashed from this happening so much, both inside and out. Have never had this type of thing occur so often in 18 years of racing.
 

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subspd said:
Just got a Stumpy FSR 29er (first FS bike!) love the bike but when cranking on high speed down hill runs the chain has a few times popped off the top gear down to the low gear causing almost death as my balance was thrown off.

Its a sram x7 front with a x9 rear and x7 shifters and GXP crank-set. I don't believe it is an adjustment issue as under "normal" operation there is never a problem. I don't seem to have any rubbing on the guides either. It only happens when I am in top gear (smallest ring in back, large ring up front).

Question.
Is it an adjustment issue anyway?
Is it because the chain is 'unloading' when hitting bumps at high speed while cranking?
Is it that I just need to get a chain guide?
Is this a FS bike problem with the chain not able to hold on under high speed compression on the rear?
Is it something else?
Sounds like design problem and/or insufficient rear der spring tension...therefore allowing the chain and rear derailleur to bounce too much.
 

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Trail Ninja
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Not everyone riding 2x10 has the problem but those with it seem to have exhausted every tuning option there is and even changed out a few expensive parts and still have the issue.

According to what I linked earlier, it seems to be the rear derailleur. I haven't changed mine out yet. Instead, I upgraded to an XX crank (since I really liked the ride of XX when I demo'd it) and that seemed to help out, but still suffers from the issue.

I'm more inclined to call up SRAM now and also complain about the issue I have with their brakes (seems one side of the caliper's pistons isn't actuating).
 
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