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  1. #1
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    How low can it go and how best to get there? A local LBS says "no way"

    Start with a stock 1987 Trek Cirrus 520. You all know where the specs are published. You've got the following spare parts to work with:
    24T chainring, 74 BCD, non-bio pace.
    NOS 14-34 Z-012 Shimano freewheel.
    NOS Suntour Cyclone GS
    New Shimano LX RD-M531 SGS
    New Uniglide 6 speed chain UG-CN51

    and as head mechanic in charge, you can sell me what you've got on hand to achieve a sub 20" gear for an upcoming ride in a mountainous area in southern Appalachia


    I asked this question because I thought I had it all worked out, but the LBS here in Austin, TX says...can't be done because....well, that's your quest: Can a sub 20" gear inch be achieved?

  2. #2
    Constant tinkerer FastJake's Avatar
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    I didn't calculate the gear inches but I see no reason this wouldn't work. What was the LBSs explanation? They don't always have a clue.

    Honestly I'd probably just throw a SRAM/KMC/whatever 6/7/8 speed chain on there with provided master link, unless you are fond of the UG chain for some reason. But if you have a new UG chain at your disposal, might as well use it.
    Why "derailer" is the correct way to spell the gear-change mechanism: sheldonbrown.com/derailer.html

  3. #3
    Senior Member Bill Kapaun's Avatar
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    As long as the OD of your tire is <28.33" or 720mm.

    24/34* tire OD

  4. #4
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    24/34 with 700cx28mm is about 20GI. what more to ask? assuming the RD can handle the chain wrap.

    OTOH i've had occasion to be "surprised" by seemingly slam-dunk mods that were big fat fail.
    Last edited by hueyhoolihan; 02-06-14 at 10:00 PM.

  5. #5
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    The UG-51 is nice since it is stock with the bike's stock UG freewheel. They're designed to work together. The 14-34 NOS is same model as stock 14-28 just more teeth. But your focus on the chain is in the area the LBS was saying. Can't guess?

  6. #6
    djb
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    I get 19 g.i. with 24/36 and 27x1 1/4

  7. #7
    coprolite fietsbob's Avatar
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    put in thousands of miles on a 13-34 7 speed , 50,40,24 triple 700-35 tires ..

    Friction bar end shifters Good..

    sun tour or a shimano chain shover will do ..

    happy to have scored closeouts when Campag dropped out of the MTB Market ..
    theyre sturdy, though like a 32 t max more than a 34..
    Last edited by fietsbob; 02-06-14 at 10:23 PM.

  8. #8
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    You should have a sub 19" gear. If you go with a mountain crank you can get a 20 and a sub 16" low.

  9. #9
    7-speed doomsday prepper ThermionicScott's Avatar
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    The math works and you can use any 6/7/8-speed chain. Don't ask us to explain why your shop is incompetent.
    Quote Originally Posted by chandltp View Post
    There's no such thing as too far.. just lack of time
    RUSA #7498

    ISO: 49T 130BCD 3/32" road chainring, preferably silver and classic-styled.

  10. #10
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    Quote Originally Posted by austex9000 View Post
    The UG-51 is nice since it is stock with the bike's stock UG freewheel. They're designed to work together. The 14-34 NOS is same model as stock 14-28 just more teeth. But your focus on the chain is in the area the LBS was saying. Can't guess?
    It should work fine.

    You don't indicate what your large chain ring size is and it might be that the LBS is concerned about the total take-up capacity of the rear derailleur (large chainring + large cog - small chainring - small cog). But in practice there's no problem exceeding the capacity as long as you avoid using the smallest chainring in conjunction with the smallest cogs. Size the chain to fit the large/large combination (otherwise a mistaken shift can result in damage) and accept that it'll hang loose if you ever happen to shift into the small/small combo.

    My tandem is set up that way and it's never been a problem since I only use the smallest chainring with a few of the largest cogs.
    Last edited by prathmann; 02-06-14 at 11:26 PM.

  11. #11
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    LBS says can't use Shimano LX RD-M531 SGS because it's a 9 speed. Wrong isn't he?

    half step.jpg

  12. #12
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    I had a mountain bike with 22x28, which is ~20". At these gear ratios you can get lower more easily by swapping to a MTB crank and taking a few teeth off the chainrings rather than adding several to the freewheel. At a certain point, exhaustion comes from total energy expenditure climbing a mountain, not wattage output. Taking aerodynamics out of the equation, which I assume is a non issue at this gear ratio, it is still the same work done if you go slow or go fast, and you've burned the same amount of calories.

    Rather than just having a really low bail out gear I prefer multiple gears so I can get a good balance of efficiency and speed. There has been times where I felt geared too low wit a bail out gear, and was more tired at the top than if I could have gotten a gear where I could get a good rhythm.

  13. #13
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    Quote Originally Posted by austex9000 View Post
    LBS says can't use Shimano LX RD-M531 SGS because it's a 9 speed. Wrong isn't he?

    half step.jpg
    Yes, 9sp Shimano mtn derailleurs will index with 7-10sp shimano road drivetrains (excepting some early duraace).

  14. #14
    Constant tinkerer FastJake's Avatar
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    Quote Originally Posted by austex9000 View Post
    LBS says can't use Shimano LX RD-M531 SGS because it's a 9 speed. Wrong isn't he?
    Oh good grief. Find a new LBS.

    And next time post this info in the OP so we aren't guessing
    Why "derailer" is the correct way to spell the gear-change mechanism: sheldonbrown.com/derailer.html

  15. #15
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    +1 on finding a new LBS.

    Or DIY. The only tough part here is swapping the freewheel (requires special tools, lotsa physical effort, and attentiveness).

  16. #16
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    Quote Originally Posted by peterw_diy View Post
    +1 on finding a new LBS.

    Or DIY. The only tough part here is swapping the freewheel (requires special tools, lotsa physical effort, and attentiveness).
    Take the wheel to a shop and ask them to take it off. Easy. Or take the wheel and the remover to an auto shop, and have them do it. (most freewheel removers are 1" hex; an air driven impact wrench is nearly perfectly suited for removing freewheels. They'll also have a big bench mounted vise, which works most of the time).

  17. #17
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    freewheels can be a PAIN to get off. I had to take the freewheel off my ex girlfriends bike, to replace the plastic spoke guard (good idea on the cheaply done SRAM derailleur it had) It took me ALL of my effort to snap that thing loose! I greased the threads well before putting it back on, in case I ever had to remove it again (nope, won't be me! )

    I recommend a BIG breaker bar...I've taken off older freewheels that were not as difficult as that 2007 Trek...
    2012 Diamondback Podium 2 - Ready for spring! :D
    1995 Specialized Rockhopper Rigid - SS converted!

  18. #18
    Constant tinkerer FastJake's Avatar
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    Best way to remove a freewheel is to put the removal tool in a vice and then use the leverage of the whole wheel. Make sure you turn it the correct way! This method has never failed me.

    Without a vice, most other methods require quite a bit of brute force. Just one of the reasons I greatly prefer cassettes.
    Why "derailer" is the correct way to spell the gear-change mechanism: sheldonbrown.com/derailer.html

  19. #19
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    i've had good success with a old 2 foot section of galvanized gas pipe. it fits nicely over my 1/2" ratchet wrench. i rarely have to hold it near the end. usually the limitation is the friction i can get from the tire and ground... i've had occasion to use my fat brother-in-law as a counterweight.

  20. #20
    Senior Member Retro Grouch's Avatar
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    There are things that I'll do on my own bike that I won't do for a customer.

    The core problem is "un-foreseen issues." Starting with a quarter century old bicycle and substituting components from different eras might work out just dandy - or not. When "not" happens (and it sometimes does) you're into the project for time and materials with no way of meeting the customer's expectations. Everybody loses.

    The next problem is how to explain it to a persistent customer who doesn't want to hear it. I've learned to simply say "I don't want to do that."
    My greatest fear is all of my kids standing around my coffin and talking about "how sensible" dad was.

  21. #21
    Junior Member
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    Quote Originally Posted by FastJake View Post
    Oh good grief. Find a new LBS.

    And next time post this info in the OP so we aren't guessing
    Hey JAKE. Shut up. I'll post when and wherever I like. Comprende?

  22. #22
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    C&V outed this one in fewer posts

  23. #23
    Old fart JohnDThompson's Avatar
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    Quote Originally Posted by hueyhoolihan View Post
    24/34 with 700cx28mm is about 20GI. what more to ask? assuming the RD can handle the chain wrap.
    If the ~20GI low is the driving criterion, and chain wrap turns out to be a problem, you can use smaller outer and middle rings to reduce the wrap requirements. You can always coast down those downhills if you don't have a high enough gear to pedal, right?

  24. #24
    Senior Member Bill Kapaun's Avatar
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  25. #25
    Constant tinkerer FastJake's Avatar
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    Quote Originally Posted by austex9000 View Post
    Hey JAKE. Shut up. I'll post when and wherever I like. Comprende?
    I was legitimately trying to help in getting you better responses. Since you have a bad attitude don't want my help, I won't reply to any more of your threads.

    Comprende?
    Why "derailer" is the correct way to spell the gear-change mechanism: sheldonbrown.com/derailer.html

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