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chain keeps running off my chainring?

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chain keeps running off my chainring?

Old 03-20-11, 01:11 PM
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sphynx_000
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chain keeps running off my chainring?

I have a cyclecross bike that I use for commuting. I converted it from a 18 to a 9 speed and am having trouble keeping the chain on when I am in the lowest gear. The chain moves off the gear towards the bottom bracket.

I have seen 1x9 speed cycle cross bikes before, so I figure this must be possible?

My chain-ring is quite worn, and I plan to replace it soon. I am wondering if the worn chain-ring could be to blame for the derailments? Or should I just convert it back to 2x9 speed?
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Old 03-20-11, 01:49 PM
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reptilezs
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extreme angle of the front ring and low gear. can you move the position of the front ring?
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Old 03-20-11, 02:00 PM
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Improving the chain line might help. You want a single ring to be as close as possible to lining up with the middle cassette sprocket for the smallest angle coming from the inner or outer sprocket.

The other consideration is if you used your old outer. That had shift gates which are designed to aid the chain in jumping off with only a nudge from the FD. Without the derailleur they are often where derailment starts. When you replace the ring buy one made for single speed or 1x? use, which won't have any shift gates.

If you still have problems, the chain itself could be a factor. Some have more bellmouth on the inner plates than others. Increased bellmouth acts like a funnel, picking up a tooth off center and guiding it home.

Worst comes to worst, you may never solve the problem if you ride on bad roads or off road. Bouncing around will cause chronis derailment. For those conditions consider either a bashwich, with guide rings on either side, or one of those chain keeper doodads that look sort of like fixed front derailleur cages. (I prefer bashwiches, but it's your call).
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Old 03-20-11, 02:30 PM
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Do inner chainrings have shift gates like the outers do?
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Old 03-20-11, 02:42 PM
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Originally Posted by sphynx_000 View Post
Do inner chainrings have shift gates like the outers do?
Ones made for the innermost position don't, because the chain is lifted off or dropped from above when shifting. But some inners have gates as a provision for use as a middle of a triple.

Gates are easy to spot, they look like cut down or missing teeth.
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Old 03-20-11, 03:56 PM
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Just ordered a new chainring and cassette. Also picked one of these "chain watchers"

If this does not work I will probably looking into a chain guide or add a bash ring.
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Old 03-20-11, 04:01 PM
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You should be fine, but you may want to consider moving the crank inboard about 4mm or so, if it's easily done. I assume you're using the ring on the outer position which is roughly 4mm of the center of the gap of the double, so moving it in will restore the original chain line. If you don't have a re-spaceable BB where you can easily move a shim don't bother unless it's necessary with the new hardware.
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