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  1. #1
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    Magic tension ratio?

    Okay... Zion frame.... 11.67" chainstay I have a 36 front ring and access to a half link, I'd like to get close to 2:1.....Any Idea's?
    Thanks

  2. #2
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    How do you get a 26" wheel in the frame? 11.67" is really short! 16" wheel?
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    The trouble with common sense is it is no longer common

  3. #3
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    oops.....16.73

  4. #4
    Sofa King We Todd Did
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    So you got a geared Zion frame? Any particular reason for that if you were going to build a singlespeed ride, when you could've picked up the EBB model for a mere $10 more?

    I'd do a search for 'SSConvert' if I were you, to try and find a link to that program that'll suggest chainring/cog combinations for you based your chainstay length.

  5. #5
    What day are we riding?
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    I like this website as you can do half-links and view the results in a chart.

    http://www.peak.org/~fixin/personal/fmu/php/formfmu.php

  6. #6
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    Results are in

    Quote Originally Posted by Guital2
    oops.....16.73
    36:18 works if your chain is worn out to 47.083"

    36:20 works for a chain of 47.057" plus a half-link

    But this is highly dependent on the accuracy of 16.73"

  7. #7
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    More variables than CS length and gear ratio....

    This question has come up quite a lot over the years, but three important variables seem to get left out of the replies. Charts like the one at peak.org are very helpful but not definitive. Real world results differ based on the variables of: 1. brand and model of chain; 2. the type of teeth on the cogs and chainrings; 3. sometimes, whether you achieve the desired ratio through a smaller cog or bigger chainwheel..

    Of the three, the first is by far the biggest factor. Though technically they shouldn't, chains vary in length even when brand new. I remember trying a 34X18 ratio on one bike. A new SRAM PC-1 was so loose it was in danger of falling off. A new KMC BMX chain of the same number of links was so tight you couldn't even force the wheel into the drops. A new SRAM PC-58 of the same number of links was just about perfect. Just a few mm here or there makes a major difference. Ideally, you find a gear ratio that you like, with components that you like, and the chain is a bit too tight when new. That gives you a heck of a lot of riding (if the chain is good quality) before it stretches to the point of concern.

    The size/profile of the teeth on the cog and chainweel have an effect also. So does the size of the cog. Really small cogs tighten the chain a bit.

    None of this is meant to discourage. In fact it's a reason for optimisim because it means that just about any bike can be converted to SS without the need for a chain tensioner. Use the Peak.org tool and from there employ some trial and error.

    Quote Originally Posted by Guital2
    Okay... Zion frame.... 11.67" chainstay I have a 36 front ring and access to a half link, I'd like to get close to 2:1.....Any Idea's?
    Thanks

  8. #8
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    Though technically they shouldn't, chains vary in length even when brand new

    Every new chain I've used has been perfect (within ability to measure). A chain isn't new unless it's just slid out of the cellophane and into your hands.

    That gives you a heck of a lot of riding (if the chain is good quality) before it stretches to the point of concern

    Useful life of a chain in a magic setup depends upon the environment. One wet ride with grit/sand can require adjustment of the chain tension. Once that happens a derailment is soon to follow unless you're cruising sidewalks.

    The size/profile of the teeth on the cog and chainweel have an effect also. So does the size of the cog. Really small cogs tighten the chain a bit.

    The type of teeth don't affect the fit, tall teeth or short teeth - the load surfaces on the teeth are 1/2" apart. The size of the chainring and cog are considered in calculations, you run into trouble if you assume 1 tooth on the chainring is equivalent to 1 tooth on the cog.

    None of this is meant to discourage. In fact it's a reason for optimisim because it means that just about any bike can be converted to SS without the need for a chain tensioner

    Just the opposite is true.

  9. #9
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    The reason I got the non EBB is because it was on Ebay for really really cheap brand new...wrong size for the guy I guess...

  10. #10
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    Folks can see for themselves...

    The chains in my example were all brand new. That's why I said they were all brand new.

    I think it's really cool the way you take a precise measurement of every new chain you buy before you use it. That investment of time and effort must really add to your cycling enjoyment.

    It is of course true that wet grit/sand conditions can increase chain wear a lot. But some chains are more wear resistant than others. And not all riders ride in these conditions -- some folks are fireroad bombers, some ride in places were it seldom rains, some try to avoid doing damage to muddy trails, some riders etc. etc. etc. Still, you make a good point that if you ride in these kinds of conditions your chain will probably wear a lot faster. That's another reason to do as I suggest and start with a chain that's a bit too tight when new.

    But the bottom line is that folks can put what I said to the test. I just offered it to be helpful, not to start a debate. The proof is in the pudding. Forget the theory and actually experiment (you know, the scientific method). Try a no-tensioner SS conversion with a new 8spd chain, a burly new BMX chain, a new some other kind of chain and see. Try a ramped cog broken out of a NOS cassette and then try, say, a Shimano BMX cog of the same tooth count. Maybe even try a wheel with a freewheel of the same tooth count.

    The differences are mainly manufacturing differences and they are small -- maybe too small for you to have noticed in your measurements -- but they exist and can make the difference when trying a no-tensioner SS conversion.

    I know because I've actually done a few.

    P.S. You've reminded me why I've been away from these forums for so long: You try to help someone only to have someone else turn it into a debate, leaving the poor newbie more confused than when he started. Meanwhile the rest of us have wasted a lot of time.

    Quote Originally Posted by pacman
    Though technically they shouldn't, chains vary in length even when brand new

    Every new chain I've used has been perfect (within ability to measure). A chain isn't new unless it's just slid out of the cellophane and into your hands.

    That gives you a heck of a lot of riding (if the chain is good quality) before it stretches to the point of concern

    Useful life of a chain in a magic setup depends upon the environment. One wet ride with grit/sand can require adjustment of the chain tension. Once that happens a derailment is soon to follow unless you're cruising sidewalks.

    The size/profile of the teeth on the cog and chainweel have an effect also. So does the size of the cog. Really small cogs tighten the chain a bit.

    The type of teeth don't affect the fit, tall teeth or short teeth - the load surfaces on the teeth are 1/2" apart. The size of the chainring and cog are considered in calculations, you run into trouble if you assume 1 tooth on the chainring is equivalent to 1 tooth on the cog.

    None of this is meant to discourage. In fact it's a reason for optimisim because it means that just about any bike can be converted to SS without the need for a chain tensioner

    Just the opposite is true.

  11. #11
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    Quote Originally Posted by singleminded
    The chains in my example were all brand new. That's why I said they were all brand new.

    I think it's really cool the way you take a precise measurement of every new chain you buy before you use it. That investment of time and effort must really add to your cycling enjoyment.

    It is of course true that wet grit/sand conditions can increase chain wear a lot. But some chains are more wear resistant than others. And not all riders ride in these conditions -- some folks are fireroad bombers, some ride in places were it seldom rains, some try to avoid doing damage to muddy trails, some riders etc. etc. etc. Still, you make a good point that if you ride in these kinds of conditions your chain will probably wear a lot faster. That's another reason to do as I suggest and start with a chain that's a bit too tight when new.

    But the bottom line is that folks can put what I said to the test. I just offered it to be helpful, not to start a debate. The proof is in the pudding. Forget the theory and actually experiment (you know, the scientific method). Try a no-tensioner SS conversion with a new 8spd chain, a burly new BMX chain, a new some other kind of chain and see. Try a ramped cog broken out of a NOS cassette and then try, say, a Shimano BMX cog of the same tooth count. Maybe even try a wheel with a freewheel of the same tooth count.

    The differences are mainly manufacturing differences and they are small -- maybe too small for you to have noticed in your measurements -- but they exist and can make the difference when trying a no-tensioner SS conversion.

    I know because I've actually done a few.

    P.S. You've reminded me why I've been away from these forums for so long: You try to help someone only to have someone else turn it into a debate, leaving the poor newbie more confused than when he started. Meanwhile the rest of us have wasted a lot of time.
    .. skipping innuendo ...

    I have experimented with a tensionless conversion. I saw it not work. Finally did the math and saw the chances of it working were small. That's why EBB's, sliding drops, ENO's, horizontal drops, singleators, etc. sell.

    Think about this: (1) Your own words say that chain length (stretch) is important. I agree! And more wear makes the magic ratio fail. (You have to put on the miles to appreciate this). (2) If the chainstay is lengthened by 1/16" it takes up 1/8" of chain slack.
    So a magic ratio is twice as sensitive to chainstay length as it is to chain length. Pick a chainstay length at random and chances are there's no magic.

    You confused the newbies with this erroneous statement "In fact it's a reason for optimisim because it means that just about any bike can be converted to SS without the need for a chain tensioner."

  12. #12
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    It really is the case that just about any bike can be converted to SS as I described (i.e. starting with a tool like that at peak.org and then employing trial and error with different components). See pics below for two of my own converted bikes. My hunch is that you didn't try enough different things in your own experiment.

    BUT, re-reading our posts, I nonetheless agree I'm guilty of misleading newbies. I should have included some information that, while obvious to me, probably isn't clear to them. I attempt to rectify things now:

    EBBs and slotted drops are certainly preferable to this kind of SS conversion for reasons that include:
    1. It can take a lot of time unless you get lucky -- a lot of trial and error.
    2. You may or may not be able to get a gear combo that you like, or that is suitable for the type of riding you want to do (i.e., the gear ratio is too easy or too hard).
    3. You may or may not have to use a gear combo that requires an unusual-sized chainweel, e.g. something other than the common 32, 34 or 36.
    4. You will have to replace the chain more often that you otherwise would, to account for chain stretch.

    I think it's great to experiment with all of this kind of stuff. I at least have found it a good learning experience. But I certainly didn't mean to imply that a no-tensioner SS conversion is some kind of nirvana.

    Finally, allow me to note that my current SS is an EBB (which is awesome!), my last had track drops and my two prior to that were no-tensioner conversions (I also had a third no-tensioner conversion a few years before them). Here are pics of the latter two, very successful conversions.
    Attached Images Attached Images

  13. #13
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    and just in case you think that Bianchi never left my backyard....

    ...here it is at SS rally several months later see (bottom right)
    Attached Images Attached Images

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