Figuring out which size cog to buy- Mtbr.com
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  1. #1
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    Figuring out which size cog to buy

    I can't believe I haven't found much info on this. I want to convert my bike to singlespeed and trying to figure out what size cog to run. I've been riding "simulated" singlespeed by picking a cog on my cassette and riding it to see how it feels. But then I read some comments about adding a tooth or two to the size you want due to not having a derailleur or something like that. So what's the best way for me to test this? Bypass the derailleur on my bike and resize the chain? Remove all cogs from the cassette but one and run an actual singlespeed but with a crappy cassette cog?

  2. #2
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    We'll need to know what kind of frame you are using. If it doesn't have an EBB or some type of tensioning style drop outs (sliding, alternator etc) you'll be running a tensioner most likely.

    I'm not sure bypassing a derailleur while its still on the frame is a good idea.

    I will say that when I was building my SS, I did the same thing with testing a geared bike for the ratio that was best. I found the tooth count I liked and have stuck with it. You may also want a separate SS chain so you can keep the one you have for gears, in case you want to throw them back on at some point.
    My bikes are faster than me.

  3. #3
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    It sort of depends on what size chainring you're using. Most people shoot for around 50 gear inches which is about a 32/18 on a 29'er.
    I brake for stinkbugs

  4. #4
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    Use this calculator: BikeCalc.com - Bicycle Gear Inches Chart

    Most people use 45-52 gear inches. For a standard 29.2.25 tire, that's usually a combo of 32/18 for flatter trails, 32/22 for super loose, steep stuff, and 32/20 for everyone else.

  5. #5
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    Buy several and try them all. I have found that only a tooth or two had a big impact on my climbing ability, how I negotiate obstacles, and overall ETs on trails. Everyone is different what works for me may not work for you, but Iím faster overall with a lower gear and thatís kind of counter intuitive.

  6. #6
    eri
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    It's not clear frm your question but you might be asking for how to find a magic ratio so you can singlespeed without an ebb, axle spiders or tensioner.

    You first need to determine approximate ratio which you do by riding your geared bike. Basically buy the hardest ratio you feel you can live with.

    Next measure chainstay length, that is the distance from center of bottom bracket to center of rear hub axle

    Then plug numbers in here:

    Javascript Bicycle Chain Length Calculator


    And fiddle ratios until you find one that's just below a whole number
    the truth is always a gift because it offers the recipient of that information the chance to change the outcome - Grace Choi

  7. #7
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    Easiest answer is yes. If you see a cog size you donít already have then yes you need that one. Not sure why but yes you need it. 😀. I kid but for real I started with the Torq lite cogs and I just bought them all. Now I play around and when I find one I like I order it in a fancier alloy version like wolftooth or endless. I know I will end up with all of them in an alloy version but this way the wife does not see $600 worth of cogs hit the front doorstep.

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