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Old 09-15-08, 09:06 AM   #1
Lalato
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Back pedaling in 1st results in chain coming off...

Hi gang,
When I'm in the lowest gear (the largest sprocket) I can't pedal backwards without the chain coming off. I've tried various adjustments, but nothing seems to help. The chain comes off at the lower part of the chainring.

The bike is an 8 speed with only one chainring up front. No front derailer. It's just a minor annoyance. It's not like I'm in 1st gear on a regular basis, but I figure I would ask to see if maybe I'm doing something wrong.

One other tidbit... the derailer is for 9 gears, I've adjusted the stops appropriately, but I'm wondering if that would affect anything.

Thanks...
--sam
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Old 09-15-08, 09:57 AM   #2
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check your hanger it might be bent.
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Old 09-15-08, 10:22 AM   #3
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Did the bike come with the single chainring, or is it a DIY job? If the single chainring is in the equivalent position as the outer chainring on a triple crank, it would still be cross-chaining, which runs the chain at a bad angle and could cause the problem you describe.
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Old 09-15-08, 03:21 PM   #4
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Hanger does not appear to be bent. Thanks for the reminder, though.

It's a folding bike. It came with the single chainring. That said, I think it's what you're describing... "cross chaining". It seems to be a bad angle that is causing the issue.

Hmmm... are there derailer's that compensate for this?

--sam
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Old 09-15-08, 05:58 PM   #5
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Don't pedal backwards. That causes the chain tension to loosen.
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Old 09-15-08, 10:15 PM   #6
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Maybe check with the dealer/manufacturer about this issue?

An alternative solution would be to use a chain guide.
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Old 09-15-08, 11:42 PM   #7
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If the chainline is set correctly, the ONLY gear that you can really backpedal in is 3rd-4th in the rear (the middle gears). ALL other gears cause the chain to bend sideways and any backpedalling will pull the chain off the chainring.
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Old 09-16-08, 05:19 AM   #8
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Danno has it right.

The rear derailleur guides the chain (from below) onto each cog. When you pedal forward, the chain stays on the cog. If you shift the derailleur while you pedal forward, the chain moves appropriately.

If you pedal backwards there is no guide for the chain (the derailleur isn't in control anymore). This is why you can't shift while pedaling backwards. When you pedal backwards the chain will automatically want to line up with the chainring. On a folding bike this problem may be exacerbated by the larger big ring and the shorter stays (if it has shorter stays).

Since the derailleur can't guide the chain when you pedal backwards you have some options:
- mount a derailleur upside down on top of the cassette (such a contraption was made to test a BB pneumatic pump using a fixed derailleur equipped bike)
- don't pedal backwards in first gear

hope this helps
cdr
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Old 09-16-08, 11:12 AM   #9
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Thanks guys... you ROCK.

For the record, I don't think I've ever pedaled backwards (in 1st) while riding the bike. I was having some rough shifting so I was "tuning" things up. The bike was up on the stand (at my local bike collective). While in 1st I noticed that it wouldn't backpedal. As noted above, I'm hardly ever in 1st here in the flatlands of Illinois... I was curious about it... and feared maybe I was doing something wrong.

Turns out I WAS doing something wrong... Don't BACKPEDAL in 1st! LOL

Thanks again for all the great info. I learn something new every day.

--sam
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