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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 09-03-10, 12:55 PM   #1
neusaab
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keep dropping my chain

Hi all. Searched to no avail. I've just converted my hardtail to singlespeed using the Forward Components EBB. I think I have the tension set pretty well, but on my first real ride I kept dropping the chain. It generally happened when climbing while hitting a bump or drop.

I maxed out the tension with temporary improvement but then the problem suddenly got quite bad and I had to bail. The chain is pretty well tight witout obvious loose or tight spots. I was able to get it back on without detensioning each time.

Any ideas on the issue? Chainline? The chainring is on the outermost position and the cog is most of the way outboard. Looks pretty straight. I'm running 44/25, with a new LX crank/outer ring, and a Shimano cassette cog with spacers on a Deore freehub. Something to do with the sizeable cog and chainring? Clumsy riding (I think not!)?

Thanks guys.
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Old 09-03-10, 01:50 PM   #2
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If anything the big cog helps you get more contact with the chain and will help you hold your chain. And if the line is straight, my guess would be your tensioner. They are really hard to set up right, you want it as close to the chainstay as possible, with the spring set pretty loose.

But you dont mention a chain tensioner, which could be an issue. If you have vertical drop out(which is probably the case) you should be running a chain tensioner, even if you try to run a "magic" ratio.
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Old 09-03-10, 02:07 PM   #3
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But you dont mention a chain tensioner, which could be an issue. If you have vertical drop out(which is probably the case) you should be running a chain tensioner, even if you try to run a "magic" ratio.
Right, no tensioner. I have one of these, which does a nice job tensioning the chain. See the link:

http://forums.mtbr.com/showthread.php?t=490528
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Old 09-03-10, 03:02 PM   #4
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maybe your cog is moving laterally under tension?
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Old 09-03-10, 03:06 PM   #5
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maybe your cog is moving laterally under tension?
Possible, I did think about that before installing the biggish cog. It's a lighter one with milling/cutouts. I might have to bite the bullet and go to 32-18 which is equivalent.
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Old 09-03-10, 03:09 PM   #6
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also, if you're able to reseat the chain without removing the wheel, it doesn't sound like you have enough tension on the chain... maybe replace a link with a half-link and retention?
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Old 09-03-10, 03:12 PM   #7
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post a picture of your setup..
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Possible, I did think about that before installing the biggish cog. It's a lighter one with milling/cutouts. I might have to bite the bullet and go to 32-18 which is equivalent.
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Old 09-03-10, 07:11 PM   #8
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I was having a similar issue a while back and thought the chain seemed plenty tight enough but it would drop on bumps or i could hear it skipping if i was really trying to climb, I just took it into my lbs and in like 5 minutes they tossed in a half link and all was solved. Haven't had an issue since. (not saying this is definitely the problem you have, just relating a similar situation. but it couldnt hurt to take it in. shrug.)
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Old 09-03-10, 08:31 PM   #9
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I think the chain tension idea is the place to start. I'm out of the adjustable range with my EBB so I'll update you once I throw in a half link. Thanks guys.
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Old 09-03-10, 08:33 PM   #10
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Before the half link. Looks pretty tight, no?
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Old 09-03-10, 11:13 PM   #11
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Its the casette cog.

There is no way that the chain is coming off because of tension issues. That chain is tighter than my fixed gear bikes and my s/s mtb. Get a s/s specific cog. You have a combo that is designed to make shifting gears easier, and with heavy torque and even slightly off chainline, off comes the chain. S/s cogs have higher/pointier teeth to engage the chain. I use a ramped chainring on my bike with s/s cogs and it's never come off.

And out of curiosity, why 44-25? Thats a bizarre choice, less than 2-1 ratio. Are you doing massive climbs? I run 34-14 and 32-16 on mine ( two rings, two cogs). Smaller chainrings give more options as well for chainline adjustment. You can move the chainring to the inside of the spider and/or get a shorter b/b to straighten the chainline.
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Old 09-04-10, 04:45 AM   #12
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Have you busted out the ruler and actually measured the chainline? That's where I would start, then worry about tension.
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Old 09-07-10, 08:31 AM   #13
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I use a ramped chainring on my bike with s/s cogs and it's never come off.

And out of curiosity, why 44-25? Thats a bizarre choice, less than 2-1 ratio. Are you doing massive climbs? I run 34-14 and 32-16 on mine ( two rings, two cogs). Smaller chainrings give more options as well for chainline adjustment. You can move the chainring to the inside of the spider and/or get a shorter b/b to straighten the chainline.
Interesting thoughts. I wondered if the chain was coming off the back, or the front which is of course heavily ramped.

Yeah, I know 44-25 is weird. It's not that weird, though. It's equivalent to 32-18, which a lot of guys around here run. We have a lot of brief but very steep climbs littered with typical New England roots and boulders which can stop you dead and bounce you off your bike. There are not a lot of fast flowy sections where taller gears would be of benefit.

I'm going to re-examine my chainline, and then consider recovering the 32t chainring that I poached for another bike to run with a different cassette cog, possibly a SS-specific one if it turns out my chainline is OK.

Thanks for your thoughts.
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Old 09-07-10, 11:08 AM   #14
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dumb question, but you're not running an 1/8 cog with a 3/32 chain right?
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Old 09-07-10, 02:03 PM   #15
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titanium is good, but chain dropping is bad.
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Old 09-07-10, 02:17 PM   #16
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I had a bike where the rear triangle was not very stiff. Whenever I would torque really hard (as when climbing) it would flex and dramatically change the chain line and drop the chain.
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Old 09-07-10, 02:47 PM   #17
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dumb question, but you're not running an 1/8 cog with a 3/32 chain right?
No dumb questions. Nah, all 9 speed stuff.
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Old 09-07-10, 03:00 PM   #18
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Have you busted out the ruler and actually measured the chainline? That's where I would start, then worry about tension.
+1

Also, if the chain is dropping inside the chainring, you could use a Deda Dog Fang on your seat tube.
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Old 09-07-10, 03:18 PM   #19
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theres also that kristin armstrong one.
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