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Thread: Cog advice...

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    Live Deliberately. davidmcowan's Avatar
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    Cog advice...

    Just picked up a set of wheels with a flipflop hub today. I've been riding with a surly cog loctite/jbwelded on a freewheel and wanted to get a flip flop in case my legs wear out on me. I've been riding 42-16 with some ease for a little under a year. These tires are lighter and thinner than my old 27's so now I'm wondering about the cogs I should get for these wheels. What brand should I use? (I won't be heading to the velodome but I do use my bike as my primary vehicle) Should I run something higher? lower? Does my freewheel side need a smaller or larger or different cog or is it all interchangeable? Will spacing the tires be a cinch or should I set aside many hours? Any suggestions for places to get good deals on these cogs?

    If you have an answer for one or all of these questions I'd be a happy man.

    Thanks...

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    Senior Member Brian Ratliff's Avatar
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    I have a Surly cog which seems pretty good. Some of the cheaper cogs seems to be offset a little so the chainline isn't perfect. I also found that a prime number of teeth on the cog (i.e. 13, 17, 19, 23) will enable you to use any chainwheel size without constantly wearing on a single patch or set of patches on tire (this is the "skid spot" that you'll hear about here).

    As for gear ratio, I currently run a 48x17, though a 46x17 (roughly like the 42x16 you currently have) was good too.
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    shoot up or shut up. isotopesope's Avatar
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    i prefer eai cogs. check out salvagetti at 1234 speer. scott carries lots of fixie stuff.

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    hello roadfix's Avatar
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    Get EAI cogs. ...no worries.
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    Senior Member mihlbach's Avatar
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    I've used EAI, Surly, and Soma cogs. I haven't been able to detect a significant difference in performance between any of these. All of them are good quality, as are Duraace and PhilWood cogs. The most important thing is not to cheap out and get a no-name or low quality cog...too many horror stories about these stripping your hub.
    As for gearing, thats a personal choice. If you are going with a free/fixed flip flop setup, its typical to gear the fixed side a little higher because you have to pedal down hills.

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    I'd like to learn more about the mathmatics of gearing. I just played around with cassette cogs on a 9 spd huub till I figured out what I wanted. The math part is probably pretty limited, but it's still very intresting. I never thought of the prime number thing before, or spreading the wear from skids with math. Thanks.
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    Quote Originally Posted by iamarapgod
    I'd like to learn more about the mathmatics of gearing. I just played around with cassette cogs on a 9 spd huub till I figured out what I wanted. The math part is probably pretty limited, but it's still very intresting. I never thought of the prime number thing before, or spreading the wear from skids with math. Thanks.
    Read this. The overall result proven (that's the sentences labelled (1) and (2)) will be clear, even if the proof isn't, as long as you know how to reduce a fraction (wikipedia will help if you forget).

    Skid Patch Theorem

    Then go here and fool around for a while.

    http://www.basementfreaks.com/members/karl/gearing/
    Last edited by mander; 02-20-07 at 07:32 PM.

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    Quote Originally Posted by mander
    Read this. The overall result proven
    That's not even close to a proof. The very first statement is already false, integers include all whole numbers, negative, positive and zero.

    Now i'd like to see someone produce a cog that has -14 teeth or 0 teeth. Pretty lame attempt if you ask me. If you're going to pretend to be smart at least do it properly.
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    Play around with a gear calculator, but you can probably push a marginally taller gear with thinner tires and lighter rims, so maybe try 42x15. As for brand, if you can buy local get whatever name brand is around (EAI, Dura Ace, Surly, whatever), if you have to buy online dura ace is great and cheap, rockwerks is rebadged surly and are also perfectly fine.

    I'm not sure what you mean by "spacing the tires." As for the freewheel size, if you want to use it to bail out on hilly terrain I would go with a 1 or 2 tooth larger freewheel, that way you can climb up in a little lower gear and then coast down. Those of us who live somewhere flatter usually go with the same gearing.
    Last edited by Landgolier; 02-20-07 at 08:19 PM.
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    Quote Originally Posted by operator
    That's not even close to a proof. The very first statement is already false, integers include all whole numbers, negative, positive and zero.

    Now i'd like to see someone produce a cog that has -14 teeth or 0 teeth. Pretty lame attempt if you ask me. If you're going to pretend to be smart at least do it properly.
    ...by acting like a prick? i didn't read the proof, but the result is clear enough and the guy did say he wanted to know more about the mathematics of gearing.

    Instead of harshing the vibe you could post in the skid patch thread and either have the guy change "integers" to "natural numbers" or explain why you think the skid patch theorem fails in the case of "impossible" cogs. The theorem is linked to off the diy sticky so that would potentially be helpful.
    Last edited by mander; 02-20-07 at 09:06 PM.

  11. #11
    Live Deliberately. davidmcowan's Avatar
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    Quote Originally Posted by Landgolier
    Play around with a gear calculator, but you can probably push a marginally taller gear with thinner tires and lighter rims, so maybe try 42x15. As for brand, if you can buy local get whatever name brand is around (EAI, Dura Ace, Surly, whatever), if you have to buy online dura ace is great and cheap, rockwerks is rebadged surly and are also perfectly fine.
    So every step down from 16 is actually a higher gear? 15 would be a higher gear? is 14 just ridiculous to try and ride around on?

    I'm not sure what you mean by "spacing the tires." As for the freewheel size, if you want to use it to bail out on hilly terrain I would go with a 1 or 2 tooth larger freewheel, that way you can climb up in a little lower gear and then coast down. Those of us who live somewhere flatter usually go with the same gearing.[/QUOTE]

    Spacing the tires was refering to getting my back cog to line up with my front chainring. Don't you have to use spacers or something? I don't know the process but I imagine it couldn't be that hard. Any links to how to do this?

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    surging w slash energy
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    the only thing from the other thread that is important:

    you just reduce the fraction of the chainring over the cog, and the denominator is the number of skid patches. If that number is odd, and you happen to skid or skip both ways (right foot forward, left foot back, and the other way around) you double the number of skid patches. There's a big difference between 34 or 38 patches vs 1 or 2.

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    On my formula hub, I have a 17t Surly cog

    On my phil fixed/fixed I have a 15t dura ace and a 17t EAI.
    I haven't had those last two cogs for too long, but I haven't heard anything bad about them.

    As for my Surly cog. No complaints. I've had it on for over a year and there is no visible wear. I've worn chainrings down, but the cog has been in nice condition.

    Don't go cheap on your back wheel.

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    Live Deliberately. davidmcowan's Avatar
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    Dura Ace seems to be the cheapest out there....is that a representation of the quality of Dura Ace? Why should I pay more for something like Surly? Wouldn't it be smarter to use the money to get myself an extra cog or two so that I can play around with them?

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    Quote Originally Posted by NNNN
    the only thing from the other thread that is important:

    you just reduce the fraction of the chainring over the cog, and the denominator is the number of skid patches. If that number is odd, and you happen to skid or skip both ways (right foot forward, left foot back, and the other way around) you double the number of skid patches. There's a big difference between 34 or 38 patches vs 1 or 2.
    The skid patch theorem says it's the # of chainring teeth whose oddness or eveness makes that difference. Is that wrong?

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    lunatic fringe Dogbait's Avatar
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    Quote Originally Posted by davidmcowan
    Dura Ace seems to be the cheapest out there....is that a representation of the quality of Dura Ace? Why should I pay more for something like Surly? Wouldn't it be smarter to use the money to get myself an extra cog or two so that I can play around with them?
    According to a mechanic at a bike shop in Portland that does a lot of work on fixed gear bikes, EAI is the best... longer wear, nice threads. Next, but close behind, comes Dura Ace. He said they will last almost as long as EAI but the difference would not be all that obvious to someone who does not ride all day, every day. He said that Surly was not worth considering due to it's being too quick to wear out... nicely made though, just too soft.

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    not actually Nickatina andre nickatina's Avatar
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    Quote Originally Posted by Dogbait
    According to a mechanic at a bike shop in Portland that does a lot of work on fixed gear bikes, EAI is the best... longer wear, nice threads. Next, but close behind, comes Dura Ace. He said they will last almost as long as EAI but the difference would not be all that obvious to someone who does not ride all day, every day. He said that Surly was not worth considering due to it's being too quick to wear out... nicely made though, just too soft.
    Just curious, which shop / mechanic?

  18. #18
    FG 48x17 eaglevii's Avatar
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    I ride a 46x16 and a 48x17, that seems pretty good to me, but Albuquerque is not super hilly within the city (not flat either). I found that anything higher than 48x17 got pretty bad in a strong headwind. Use a gear inches calculator to get an idea of how much of a difference these would be from your current set up. As someone else mentioned, if you have a road bike, find cog/chainring combos that match the gear inches/gain ratio of the fixed ratio you are contemplating, and try it out.

    I've used IRO and Surley cogs, both with good results. Be sure to get the correct width cog, in my experience Dura Ace 1/8" cogs are a little thinner than others, and can be mistaken for 3/32" by some know nothing LBS workers.

    On my bike that has a freewheel, I went with the same size as the cog, because I enjoy that ratio. I think it would be more practical to make it a little larger, since you'll be using it when you're tired.

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    lunatic fringe Dogbait's Avatar
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    Quote Originally Posted by andre nickatina
    Just curious, which shop / mechanic?
    I don't know the mechanic's name but the shop is Bike Central.

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    not actually Nickatina andre nickatina's Avatar
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    Could very well be Dean than, that guy's legendary.

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    Quote Originally Posted by mander
    The skid patch theorem says it's the # of chainring teeth whose oddness or eveness makes that difference. Is that wrong?
    Looking at each column in the table I would say it is the cog not the chainring.

    EDIT: I was thinking about this a bit more. The best way to maximize the number of skid patches is to use a chainring and a cog that are prime numbers this will give you a total number of skid patches equal to the number of teeth on the cog. Since the max number of skid patches one can have can not be greater than the number of teeth on the cog, I would say the cog dominates.

    However, upon further inspection I also realized that one can have a cog that is not prime but does not divide the chainring and still obtain skid patches equal to the number of teeth on the cog. In other words the cog and the chainring will maximize the number of skid patches if they are relatively prime.
    Also, I just found this.
    Last edited by lvleph; 02-21-07 at 05:42 AM.

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    jack of one or two trades Aeroplane's Avatar
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    Quote Originally Posted by Dogbait
    He said that Surly was not worth considering due to it's being too quick to wear out... nicely made though, just too soft.
    Surly drastically changed their cogs a couple years ago. They are now much higher quality, and wear very well.
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    aka mattio queerpunk's Avatar
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    Quote Originally Posted by operator
    Now i'd like to see someone produce a cog that has -14 teeth or 0 teeth.
    i've produced a 0 tooth cog.

    it's sitting on your desk right now.

    here's a picture of it:
    the hipster myth.

    i practice vagabondery.

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    Quote Originally Posted by operator
    That's not even close to a proof. The very first statement is already false, integers include all whole numbers, negative, positive and zero.

    Now i'd like to see someone produce a cog that has -14 teeth or 0 teeth. Pretty lame attempt if you ask me. If you're going to pretend to be smart at least do it properly.
    Nice try but you lose.

    Just because a -14 tooth cog doesn't exist does not effect the validity of the proof. Since the set of real world situations is a subset of those for which the proof is valid it is fine.(If you really wanted to you could think of a negative gear ratio one in which the chain was crossed.)

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    Quote Originally Posted by dutret
    Nice try but you lose.

    Just because a -14 tooth cog doesn't exist does not effect the validity of the proof. Since the set of real world situations is a subset of those for which the proof is valid it is fine.(If you really wanted to you could think of a negative gear ratio one in which the chain was crossed.)
    +Group theory*
    Last edited by lvleph; 02-21-07 at 08:28 AM.

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