forgot my geometry book (chain length ?)- Mtbr.com
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  1. #1
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    forgot my geometry book (chain length ?)

    i am meditating on one of those great geometry questions that seems like it should have a simple/obvious answer. however, i am also aware that the simple/obvious answer is not always the right one. here goes:

    if i run a single speed set up (38fX17r) and i change the ring size of the front ring down two teeth to a 36, would i need to increase the rear cog by two teeth to a 19 to keep the same chain length? i am pretty certain that the ratio will change (not sure by how much, but i do have the ratio chart at home, so i can look that up). my concern here is how to keep the same chain length.

    thanks.

  2. #2
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    you can use the same number of links but most likely will have to re-adjust the tension; there is a difference but its very small. Unless you are already set toan extream on the dropout, there shouldnt be any need to drop/add links.

    Of course, the best way is to simply do it and find out...
    Quote Originally Posted by Gunslingger
    no doubt you must have majored in english or something rad!!!

  3. #3
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    that is what i thought

    Quote Originally Posted by zedro
    you can use the same number of links but most likely will have to re-adjust the tension; there is a difference but its very small. Unless you are already set toan extream on the dropout, there shouldnt be any need to drop/add links.

    Of course, the best way is to simply do it and find out...
    i love to single speed. i hate being limited to one gear choice all the time when i have one long climb up and one long ride back down. i am a cheap bastard and don't want to spend $$$ on a front and/or rear der. i have a plan to do the following:

    1 - get an evil DOC.
    2 - get one of the bashguards that mounts to the middle of a three ring set up with a thin outter guide plate outside of the big ring. they let you run a big gear and a granny gear (you need to change rings by hand). i forget the company that makes these, but i know the link is on nsmb.com
    3 - figure out a good gear spread that uses the same net number of teeth on the front and rear (eg 22X30 and a 38X14).
    4 - rig it so that i can single speed in the lower ratio up a long climb. then do a manual ring change to the higer ratio set of gears at the top of the hill and run back down hill without spinning out as much.

    i think this can be done pretty easily. it should not be too big a pain to change rings on the evil DOC due to the dropout set up (easy to de- and re-tension). the cogs in the back can be spaced out with spacers (what else) well enough to keep a good chainline in each of the two gearings.

    am i mad, or does my two speed setup sound like it would work? i think it will, and it will be fun.

  4. #4
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    Quote Originally Posted by mandown
    am i mad, or does my two speed setup sound like it would work? i think it will, and it will be fun.
    i think i've heard of peeps doing this. I dont see a problem since you'll have to loosen your dropouts anyways to change gears. You might have to use an odd spacer size between the rear cogs; BB shell spacers work well for this and can be had in small increments.
    Quote Originally Posted by Gunslingger
    no doubt you must have majored in english or something rad!!!

  5. #5
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    might not work since you are a self confessed cheap bastard but here in an option.

    http://whiteind.com/ENO_web/freewheel2.html
    http://whiteind.com/ENO_web/cranks2.html

    you can even use them together for ultimate versitility. Not sure how they would stand up to serious abuse though.

  6. #6
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    Quote Originally Posted by FrontRanger
    might not work since you are a self confessed cheap bastard but here in an option.

    http://whiteind.com/ENO_web/freewheel2.html
    http://whiteind.com/ENO_web/cranks2.html

    you can even use them together for ultimate versitility. Not sure how they would stand up to serious abuse though.
    thanks man. cannot wait to see the photos of how that bad boy works.

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