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  1. #1
    Senior Member sonnetg's Avatar
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    Rear Derailluer failure - [temporary single speed conversion possible?]

    Hello,

    I am curious whether this may be possible or not. Is it possible to carry around a spare chain and fit it on your bike when or if you have a derailleur failure on the road? This is not a permanent solution, but more like a temporary fix so you can at least reach your destination. The gears wont work if you take the rear derailleur out of the mix, but I will still be able to pedal to my destination.

    I have a few questions on converting to single speed without removing the cassette:

    -> Does the rear cog have to perfectly aligned with the chain ring?
    -> Do I need a chain tensioner?

    The reason I am asking is because I ride trails and roads a lot, and no matter how careful i am, I seem to either bang it or smash the rear derailleur with on thing or another on the road or trail. I am seriously contemplating on switching to a internal hub gear, but for now, I need to work with what i have.

    Any advice would be greatly appreciated.

    Thank you,
    Last edited by sonnetg; 03-29-11 at 08:30 AM.

  2. #2
    Subjectively Insane MilitantPotato's Avatar
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    Sometimes.
    You need to find a combination that has just enough slack to prevent out-of-round chainrings and cogs from binding, and not so much that the chain skips or derails itself.

    If your bike has such a gear combo, and it's not badly cross-chained, you're in luck. If not, carry a chain tensioner. Use a chain-stay mounted tensioner, in case you bend/break the hanger.
    You've got a bike, so you gotta move.

  3. #3
    Senior Member sonnetg's Avatar
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    Quote Originally Posted by MilitantPotato View Post
    Sometimes.
    You need to find a combination that has just enough slack to prevent out-of-round chainrings and cogs from binding, and not so much that the chain skips or derails itself.

    If your bike has such a gear combo, and it's not badly cross-chained, you're in luck. If not, carry a chain tensioner. Use a chain-stay mounted tensioner, in case you bend/break the hanger.
    Hello, Thanks for the advice. I have managed to damage the rear derailleur/hanger twice within a year. The first time I was able to hand straigten it and limp back home, but the 2nd time, the derailleur got caught with a twig and snapped. I had to walk 5-7 miles and reach my destination. (see the images below).

    prevent out-of-round chainrings and cogs from binding,
    I know few basics of bike mechanics, but can you please expalin "out-of-round" chairing? And what exactly is binding?

    I plan to keep carry a cheap/spare chain with me, so that i can isntall it on spot and ride as if it were a single speed bike. I prefer not to use chain tensioner, as this is meant to be temporary. I guess I need to give it try, but I really dont know how much chain tension would be appropriate, or whether you can have the perfect tension without a chain tensioner? I guess I will have to give it a try and experiment with it.

    I will try my best to keep the chain aligned with the chainring and the cogs, so i hope i dont have to deal with annoying clicking noise or, worse, the chain coming off/deralling.
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  4. #4
    coprolite fietsbob's Avatar
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    Chain tool is required.. not necessarily a spare chain. believe me,
    if the chain breaks and comes off,
    you will not travel but a yard/meter or so, then can walk back and pick it up.
    OTOH, a few spare links.. may be useful..

  5. #5
    Senior Member sonnetg's Avatar
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    Quote Originally Posted by fietsbob View Post
    Chain tool is required.. not necessarily a spare chain. believe me,
    if the chain breaks and comes off,
    you will not travel but a yard/meter or so, then can walk back and pick it up.
    OTOH, a few spare links.. may be useful..

    Yes. I have a chain-tool that comes with my Pedros multi-tool. I absolutely carry spare links as well. ( As for the spare chain, I was hoping a cheap backup chain, which i can use for emergencies only, and not damage the original, but it does make sense not to carry the extra weight.)

    Here's my emergency kit. Carrying a spare RD would be a bit too much.
    Last edited by sonnetg; 03-29-11 at 09:47 AM.

  6. #6
    motovation frankenmike's Avatar
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    Chain tool is all you need. If RD breaks, break the chain to as tight as possible on the straightest chainline possible. Probably will not be perfectly tensioned, but the straight chainline should keep the chain on good enough so you can at least limp home(you will have to put the chain back on a couple times). I've had to do this several times. Hopefully you will never have to do this! Cheers

  7. #7
    Senior Member sonnetg's Avatar
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    Quote Originally Posted by frankenmike View Post
    Chain tool is all you need. If RD breaks, break the chain to as tight as possible on the straightest chainline possible. Probably will not be perfectly tensioned, but the straight chainline should keep the chain on good enough so you can at least limp home(you will have to put the chain back on a couple times). I've had to do this several times. Hopefully you will never have to do this! Cheers
    It makes sense, but why does the chain have to be in a straight line or perfectly aligned? I should be able to align cog with the chainring, but it probably wont be the most comfortable settings. Also, when using a derailleur, isn't the the chain slightly misaligned?

    I guess, I will try to keep the chain straight. Forget being comfy...anything is better than walking.

    As for the chain tension, I will try to keep the least slack as possible. Hopefully, it wont some off frequently.

    Thanks.

  8. #8
    Senior Member BCRider's Avatar
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    The "out of round" bit mentioned above is just the typical mechanical tolerances found in the bike's gearing. On a true single speed or fixie the small amounts of this out of roundness due to various tolerance build ups gives you a a few spots where every few crank rotations the chain actually goes quite tight if you don't give it just a little slack.

    In your emergency situation any combination that will actually let you install the chain is likely to be fine. But if it should come up you want a combo that has a touch of slack rather than one that is guitar string tight.

    And as mentioned already you don't need a spare chain. The one on the bike has more than enough to build a single speed chain from to get you out of the woods or over the hill. In fact I'd say that you'd be fine without even having a small section of a few spare links. It's hard to imagine ripping the chain apart enough to ruin enough that there would not be enough to join to get back.

    Note that you'll be cutting and joining the chain on the road/trail in an emergency situation. As such you'll likely be using the original pins re-installed. This is generally not seen as being a good way to do things as such links will never be as strong as originally. The solution for this is to either bring along a half dozen servicing pins if it's a Shimano chain or a few master links if it's a SRAM or KMC. Having those will give you what you need to put back together even a badly damaged chain that got torn and mutilated in even two spots. On the other hand I remember a time on my single speed commuter where I "temporarily" joined a chain using an original pushed out pin and then ended up riding the darn thing for about a month before I remembered to get around to the shop and buy a new chain for it. So re-using a pin and link isn't automatically a recipe for instant disaster.
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  9. #9
    Senior Member sonnetg's Avatar
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    The "out of round" bit mentioned above is just the typical mechanical tolerances found in the bike's gearing. On a true single speed or fixie the small amounts of this out of roundness due to various tolerance build ups gives you a a few spots where every few crank rotations the chain actually goes quite tight if you don't give it just a little slack.
    So, "out of round" is basically a chainring, which is out of true? Never thought of it, but I guess it could happen.

    But if it should come up you want a combo that has a touch of slack rather than one that is guitar string tight.
    How much slack? Any way to measure it? 1/4" or 1"?

    Note that you'll be cutting and joining the chain on the road/trail in an emergency situation. As such you'll likely be using the original pins re-installed. This is generally not seen as being a good way to do things as such links will never be as strong as originally.
    I have broken chains before to install rear derailleurs, and never had any issue, but I do agree the broken link is no longer the same strength as new. It may break any time without warning. I now use master links, which is really a life & time saver.

    The solution for this is to either bring along a half dozen servicing pins if it's a Shimano chain or a few master links if it's a SRAM or KMC. Having those will give you what you need to put back together even a badly damaged chain that got torn and mutilated in even two spots. On the other hand I remember a time on my single speed commuter where I "temporarily" joined a chain using an original pushed out pin and then ended up riding the darn thing for about a month before I remembered to get around to the shop and buy a new chain for it. So re-using a pin and link isn't automatically a recipe for instant disaster.
    Agreed 100%. I had no idea you could purchase the links. I need to look for it.

    Thanks for such great advise.

  10. #10
    motovation frankenmike's Avatar
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    Quote Originally Posted by sonnetg View Post
    It makes sense, but why does the chain have to be in a straight line or perfectly aligned? I should be able to align cog with the chainring, but it probably wont be the most comfortable settings. Also, when using a derailleur, isn't the the chain slightly misaligned?

    I guess, I will try to keep the chain straight. Forget being comfy...anything is better than walking.

    As for the chain tension, I will try to keep the least slack as possible. Hopefully, it wont some off frequently.

    Thanks.
    The straight chainline is to keep the semi-loose, albeit shortened, chain on the cog. After all, there is no longer a derailer to keep an angled chainline on the cog. And yes, comfort is no longer a concern- getting out of the woods without walking ten miles is.

  11. #11
    DRF aka Thrifty Bill wrk101's Avatar
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    Get a bash guard for the rear derailleur instead. They are cheap.

  12. #12
    Senior Member BCRider's Avatar
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    On a properly set up single speed or fixie the amount of slack at the mid point would be around 1/2 to 3/4 inch of movement if you lift up and push down the chain where the ring runouts at front and rear produce the tightest spot. So that would be your least amount of slack or "tension". But I'd expect that you can get away with the lower run hanging down loose by up to about 2 inches in an emergency. With that much slack you can expect to throw the chain a few times on the way back in the rougher stuff but you'll make it back eventually.

    As for that wobble? Trust us, they ALL wobble a small amount. You just never notice it until you put together a fixie or single speed. It comes from the chain teeth maybe not being cut truly to the center or just in how the ring mounts to the crank arm or from the odd bash to the ring in use. But they all wobble a little. Same at the rear. Freewheels and cassete/freehubs seldom run truly on center. The total front to rear may only be a small amount that you need good guages for but when you're talking about a fixed length drive chain it only takes a total path length variation of a mm or two at most to go from a proper slack to guitar string tight chain.
    Last edited by BCRider; 03-30-11 at 12:08 PM.
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  13. #13
    Senior Member sonnetg's Avatar
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    Quote Originally Posted by wrk101 View Post
    Get a bash guard for the rear derailleur instead. They are cheap.
    Bash guards are good if you fall of or hit a rock or something. But what happened in my case, and i am still a baffled....it was a twig or maybe a root which got sucked in to the chain and the RD causing this damage. I am not sure whether the Bash Guard would have helped, but I do see how useful these guards can be. I have to check my MTB whether or not if has the brazeons for the guard.

    I am seriously contemplating on converting my MTB to a single speed or, at least, installing a Nexus 7 speed internal hub gear. It ain't cheap replacing and maintaining these rear derailleurs.

    Thanks for the advice though.
    Last edited by sonnetg; 03-30-11 at 03:17 PM.

  14. #14
    Senior Member sonnetg's Avatar
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    Quote Originally Posted by BCRider View Post
    On a properly set up single speed or fixie the amount of slack at the mid point would be around 1/2 to 3/4 inch of movement if you lift up and push down the chain where the ring runouts at front and rear produce the tightest spot. So that would be your least amount of slack or "tension". But I'd expect that you can get away with the lower run hanging down loose by up to about 2 inches in an emergency. With that much slack you can expect to throw the chain a few times on the way back in the rougher stuff but you'll make it back eventually.

    As for that wobble? Trust us, they ALL wobble a small amount. You just never notice it until you put together a fixie or single speed. It comes from the chain teeth maybe not being cut truly to the center or just in how the ring mounts to the crank arm or from the odd bash to the ring in use. But they all wobble a little. Same at the rear. Freewheels and cassete/freehubs seldom run truly on center. The total front to rear may only be a small amount that you need good guages for but when you're talking about a fixed length drive chain it only takes a total path length variation of a mm or two at most to go from a proper slack to guitar string tight chain.

    Thank you. This really helps to have a somewhat estimation of how much tension I should try to achieve. I might actually convert one of my bike to a single speed just for MTB and off roading.

    This site really helped with many questions i had: http://www.mtbr.com/ssfaqcrx.aspx


    I am also curious, whether there are there any sites or LBS that sell single speed MTBs one with internal hubs? I wasn't much into MTBing, but I can see why there is such a craze for it :-)

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