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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 02-28-09, 08:54 PM   #1
jzsoup
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Ate pavement on my new SS build

So (I thought) I finished my SS build this week. I took it out for a quick spin around the block before I left for work. Started cranking on it pretty hard and the chain came off the ring and I ate s*** like never before. All scraped up, hit my head on the asphalt, etc. (No sympathy from wife).

Anyway, I used a Bontrager road crank and just removed the large ring so I'm running the 39 tooth. I've got a 13 tooth cog in the back from an old road cassette I took apart. I'm using what I believe to be a 1/8" chain from my spare parts box. The tension seems decent, but I'll try to put in a half link as soon as I can find one (frame has vertical dropout).

Now I'm asking your suggestions....is this a chain tension issue? Or is there a problem running a chain ring designed for shifting? (i.e. the teeth aren't tall enough?) Any guidance is appreciated.
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Old 02-28-09, 09:14 PM   #2
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im not really sure about the chainring designed for shifting, but some of my friends tell me that their chains have occasionally popped off when their tension was a bit too loose, so it very well could be a tension issue
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Old 02-28-09, 09:22 PM   #3
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If you're running it SS but not fixed, you might be better off installing a chain tensioner to help with that. Glad you're OK, sounds pretty cruddy for a first trip out.
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Old 02-28-09, 09:25 PM   #4
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Make sure your drivetrain is all the same size... Thats my only guess.
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Old 02-28-09, 09:31 PM   #5
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That 13 tooth cog is only going to engage 6.5 teeth and with the shorter teeth it will not hold a chain as well as a proper ss cog...I have used 14 tooth cogs off of cassettes in the past and they really are not the way to go if you are going to hammer things.

Add a little chain slack or a rear wheel that isn't well secured and the recipe for disaster starts looking pretty complete.

I run normal 3/32 chain rings in most of my fg bikes with no issues but my rear cogs are all ss / fg specific, and my chain lines and tensions are perfect.

Check your chain line and chain tension, make sure the alignment is dead on and consider running a larger chain ring / cog combination for your preferred gearing.

Most important of course is that you are okay.
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Old 02-28-09, 09:32 PM   #6
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I use a Shimano Ultegra 42 chain ring meant for shifting and over 2 years have never had a problem with it coming off, get a tensioner and you will be fine.
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Old 02-28-09, 09:32 PM   #7
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Whoops... I just saw the vertical dropout bit.

Forget the half link... you need a chain tensioner.
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Old 02-28-09, 09:39 PM   #8
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Yesterday on my way home from work I decided to skip stop up to a light instead of braking, and my chain hopped right off. Turns out my "Ehhh, it'll be fine until I get home" tension wasn't quite enough. Not only was I glad I had a brake, but I learned to always get that chain tensioned up, because next time I might not be so lucky as to just keep rolling.

Yeah, get a tensioner. You'll be glad you did.
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Old 02-28-09, 09:49 PM   #9
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i had my chain fall off due to tension once and it ended up costing me because it caused the rear wheel to lock and i skidded right through a tire
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Old 02-28-09, 10:17 PM   #10
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Thanks for sharing your experience. There's literally no one in my town to ask about SS/FG. I'm going to improvise a tensioner tomorrow out of an old rear derailleur while I shop for something a that looks a little cleaner. I may also tinker with putting on the 53 tooth ring and a larger cog; you know, just because I can.

Thanks everyone.
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Old 02-28-09, 10:19 PM   #11
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i had my chain fall off due to tension once and it ended up costing me because it caused the rear wheel to lock and i skidded right through a tire
This happened to a friend of mine because he decided to loosen his chain way up for some reason, except it was lucky as hell because he was bombing a hill with no brakes at the time.
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Old 02-28-09, 11:21 PM   #12
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All you need is a tensioner to prevent the chain from flying off.
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Old 02-28-09, 11:37 PM   #13
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Originally Posted by jzsoup View Post
Thanks for sharing your experience. There's literally no one in my town to ask about SS/FG. I'm going to improvise a tensioner tomorrow out of an old rear derailleur while I shop for something a that looks a little cleaner. I may also tinker with putting on the 53 tooth ring and a larger cog; you know, just because I can.

Thanks everyone.
Just use the old derailer as is... there is no better tensioner out there than this.
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Old 03-01-09, 05:07 PM   #14
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Threw on an old rear derailleur this afternoon; problem solved. I prefer the look without a tensioner, but what can you do? The bike has to have one in order to be rideable. Thanks for all the help!
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Old 03-01-09, 06:22 PM   #15
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bummer dude hope you recover quick....i too a couple spills yesterday too haha
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Old 03-01-09, 06:32 PM   #16
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i dont think anyone mentioned it, but is your chainline bad?
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Old 03-01-09, 08:03 PM   #17
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I bet, its the teeth on the rear cog , esp. if its from a cassete ... its designed, to have the chain climb off of it easy . ( the teeth are shorter & have little ramps in the side and some of the teeth are twisted a bit. )

A ss/kit tensioner might band-aid your isue, but it wont fix its cause ...

Kinda like balancing a bent ( car ) wheel .. you can put weights on it & it will "balance-out" on the fantsy computerized spin balancer ... but I bet it will still shake and vibrate the car like crazy. ( since it doesent straithen the wheel. )

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Old 03-01-09, 09:25 PM   #18
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i dont think anyone mentioned it, but is your chainline bad?
Chain line is good.
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Old 03-01-09, 09:29 PM   #19
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If you wanted to be really sure, get a 3/32" singlespeed chain (specifically singlespeed - less lateral flex), a large (maybe 17t) BMX cog, and a 48t singlespeed ring. You're probably just fine with a derailer-as-tensioner though.
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